The geomorphology of the Florida Peninsula ( FGS: Bulletin 51)

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Material Information

Title:
The geomorphology of the Florida Peninsula ( FGS: Bulletin 51)
Series Title:
Geological bulletin
Physical Description:
x, 164 p. : illus., 7 fold. col. maps (in pocket) ; 24 cm.
Language:
English
Creator:
White, William Arthur
Florida -- Bureau of Geology
Publisher:
Published for Bureau of Geology, Division of Interior Resources, Florida Dept. of Natural Resources <by Designers Press, Orlando, Fla.>
Place of Publication:
Tallahassee
Tallahassee

Subjects

Subjects / Keywords:
Geomorphology -- Florida   ( lcsh )
Genre:
bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Bibliography: p. 161-164.
Additional Physical Form:
Electronic version available on the World Wide Web as part of the Linking Florida's Natural Heritage Collection.
General Note:
Errata slip inserted.
Statement of Responsibility:
by William A. White.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:

The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
ltqf - AAA0297
notis - AED9138
alephbibnum - 000843151
oclc - 00828144
lccn - 73622680
System ID:
UF00000149:00001


This item has the following downloads:


Table of Contents
    Title Page
        Page i
        Page ii
    Errata
        Page ii-a
        Page ii-b
    Letter of transmittal
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
    List of Illustrations
        Page vii
        Page viii
        Page ix
    Acknowledgement
        Page x
    Delineation of geomorphic features
        Page 1
    Major geomorphic divisions of the Florida Peninsula
        Page 2
        Page 3
    The Distal or Southern Zone
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 30a
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
    The Midpeninsular Zone
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
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        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 140a
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
    The Proximal or Northern Zone
        Page 155
        Page 156
        Page 157
        Page 158
        Page 159
        Page 160
    Bibliography
        Page 161
        Page 162
        Page 163
        Page 164
    Plates
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
        Page 170
        Page 171
        Page 172
        FGS
        i
        ii
        iia
        iib
        iii
        iv
        ix
        v
        vi
        vii
        viii
        x
Full Text

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES



BUREAU OF GEOLOGY
Robert O. Vernon, Chief



GEOLOGICAL BULLETIN NO. 51



THE GEOMORPHOLOGY
OF THE FLORIDA
PENINSULA




By
William A. White







Published for
BUREAU OF GEOLOGY
DIVISION OF INTERIOR RESOURCES
FLORIDA DEPARTMENT OF NATURAL RESOURCES






Tallahassee, Florida
1970






DEPARTMENT
OF
NATURAL RESOURCES




CLAUDE R. KIRK, JR.
Governor


TOM ADAMS
Secretary of State




FLOYD T. CHRISTIAN
Commissioner ofEducation




FRED O. DICKINSON, JR.
Comptroller


BROWARD WILLIAMS
Treasurer




EARL FAIRCLOTH
Attorney General




DOYLE CONNER
Commissioner ofAgriculture


W. RANDOLPH HODGES
Executive Director






GEOLOGICAL BULLETIN NO. 51


ERRATA

Please attach this errata sheet to the inside cover of Bulletin No.
51.

PAGE
III 2nd par., 2nd line "Florida" not "florida."
19th line lineamentss" not "lineamounts."
V Line 34 "Lines" not "Liens."
VI Line 18 "Aeolian" not "Aeolean."
VI Line 18 "Peninsula" not "Peninsual."
Last line "Bibliography" not "Biography."
VIII Titles for figures 32 and 33 should bear the acknowledgement, "After Davis
(1946)".
Figure 43 3rd line "Caloosahatchee" not "Caloosahattchee."
2 2nd par., 3rd sentence et seq. should read as follows:
"The central or mid-peninsula zone extends northward from this line as far
as one which would pass approximately through the cities of St. Augustine,
Palatka, Hawthorne and Gainesville. From this last line the northern or
proximal zone extends northward to Georgia."
4 1st par., next to last line "Post-Flandrian" not "post-Floridian."
Sub-heading "Peculiarities" not "Pecularities."
10 1st line "attested" not testeded"
11 Figure 3 should bear this legend "Contours show elevation above assumed
datum in inches."
12 Figure 4 should bear legend saying that length of line indicates number of
observations. Arcs are drawn at distances indicating 6, 9, and 10
observations.
7th line in par. "Caloosahatchee" not "Caloosahattchee."
22 2nd par., 3rd line "their" not "then."
26 2nd par., 2nd line from bottom "accretions" not "acretions."
31 5th line from bottom "instances of such" not "instances such."
32 2nd sentence "lose their coast-perpendicular" not "loose their
coast-parallel."
35 Figure 16 should bear the following legend:
0 to 5 fathoms

/ / 5 to 10 fathoms

I : sandy bottom

42 2nd par., 4th line "is" not "in."
6th line from bottom of page "islands" not "inlands."
43 2nd par., 4th line "lee" not "Lee."
51 5th line delete reference to figure 25.
66 1st par., 4th line "27" not "28."
71 Figure 29 should bear this legend: "Contours show elevation above assumed
datum in inches."






ERRATA, cont.


PAGE

73 Figure 30 should bear this legend: "Contours show elevation above assumed
datum in inches."
80 Figure 32 should bear the acknowledgement: "After Davis (1946)."
81 Figure 33 should bear the acknowledgement: "After Davis (1946)."
91 2nd par., 7th line "coast-parallel" not "coast parallel".
3rd par., 12th line sentence should read: "Their pattern on the map
suggests that they originally converged to make an early counterpart of the
present False Cape."
4th par., 4th line "Mayport" not "Maysville."
94 2nd par., 5th line "traverse" not "transverse."
95 4th par., last line "figure 41" not "figures 40 and 42."
104 4th par., 5th line "coast-parallel" not "coast parallel."
122 Both references to Bishop are to his 1956 publication, not 1959.
3rd line from bottom "Hawthorn" not "Hawthorne."
123 3rd line of sub-heading "Crescent" not "Cresant."
125 The line of alternate dots and dashes referred to in the next-to-last sentence
of the first paragraph under the heading "POSSIBILITY OF A RELICT
CAPE AT ORLANDO" was omitted from Plate 1.
127 4th par., 6th line "gingerly" not "ginerly."
133 Heading "WESTERN" not "WESTER."
4th par., 3rd line "cross" not "corss."
4th par., 4th line "valleys" not "valley."
135 4th par., 4th line "juncture" not "junture."
137 3rd par., 7th line "southern" not "solution."
139 3rd par., 5th line "apophyse" not "apoplyse."
152 1st par., 12th line "is" not "in."
1st par., 14th line foreste" not "foresee."
155 1st par., 1st line "Miocene" not "miocene."
156 4th par., last line "Okefenokee" not "Okefenoke."
5th par., 5th line "subterranean" not "subteranean."
157 4th par., 10th line "subterranean" not "subteranean."
158 2nd par., 3rd line "Okefenokee" not "Okefenoke."
2nd par., 7th line "Okefenokee" not "Okefenoke."
3rd par., 5th line "Okefenokee" not "Okefenoke."





LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
May 7, 1970

The Honorable Claude R. Kirk, Chairman
Department of Natural Resources
Tallahassee, Florida

Dear Governor Kirk:
The Bureau of Geology of the Division of Interior Resources is
printing as its Geological Bulletin No. 51 a report prepared by Dr.
William A. White, professor of Geology at the University of North
Carolina on "The Geomorphology of the Florida Peninsula."
This report was originally started as part of a six volume series
on the geology of florida, but because of budgetary limitations the
portion on the panhandle of Florida was not completed in time to be
included with this publication. It is planned to subsequently issue the
companion report on the Geomorphology of the Florida Panhandle
and to combine these two as a volume in a set that will ultimately
include under "The Geology of Florida" volumes on the stratigraphy
of Florida, the water resources of Florida, the structure of Florida,
guide fossils of Florida, and perhaps a volume on geochemistry.
In order to protect the names assigned by Dr. White it was felt
desirable to publish his report immediately.

Respectfully yours,


R. O. Vernon, Chief
Bureau of Geology

ROV:ebl

























































Completed manuscript received
December 15, 1969
Published for the Bureau of Geology
Division of Interior Resources
Department of Natural Resources
By Designers Press
Orlando, Florida



iv





CONTENTS



Acknowledge ent ...............................................x
Delineation of Geomorphic features .................................1
Major Geomorphic Divisions of the Florida Peninsula .................... .2
The Distal or Southern Zone ........................................4
Major peculiarities of the Southern Part of the Florida Peninsula ........ .4
The Florida Keys ............................................15
The High Coral Keys ....................................... 15
The Low Coral Keys and the Oolite Keys .................. .... .19
Florida Bay .................................................32
The Islands and Shoals of Florida Bay ..........................24
Drainage of the area adjacent to the north shore of Florida Bay ... 30-31
The Lower west coast of the peninsula ............................ 33
The Ten Thousand Islands ................................. 43
The Silver Bluff Ridge and Scarp ................................43
The Miami Ridge ............................................ 58
Relict Mangrove Islands ....................................59
The Everglades ..............................................68
Deposition around the edge of the Everglades .................... .72
Influence of structural lineamounts on solution
in the Distal Zone of the Peninsula ........................... 75
Lakes around the edge of the Everglades Trough .................. .78
Reasons for different kinds of Swampy Surface in the Distal Zone .... 82
The Imokalee Rise ...........................................84
The Midpeninsular Zone .........................................85
The Atlantic Coastal Lowlands .................................. 85
Atlantic Coastal Ridge, Lagoons and Barrier Chain ................ 85
The Eastern Valley ..........................................93
The St. Johns River Lake Chain ...........................102
St. Johns River Offset ................. ................... 104
History of the Econlockhatchee River ...................... .108
Southern end of the Eastern Valley ......................... 109
The Saint Mary's Meander Plain .............................. 110
The Central Highlands ....................................... 110
Origin of Liens of Lakes in ridges of the Central Highlands .........114
The Lake Wales Ridge .................................... 119
The Intraridge Valley ...................................119
The Higher parts of the Lake Wales Ridge .................... 120
Genetic Relation between Lakes Karst and Relict shoreline
features in Deland and Crescent City Ridges, Geneva
Hill, and the Osceola Plain ............................... 123
Possibility of a relict cape at Orlando .................... ..125
The Marion Upland and the Mount Dora Ridge ................. .128






The Brooksville Ridge ..................................... 128
The Fairfield and the Ocala Hills .............................130
The Cotton Plant Ridge ............................... .... 130
The Lake and Sumter Uplands .............................. 131
The Polk Upland ..........................................132
The Western and Central Valleys ............................ 133
The Western Valley ..................................... 133
The Zephyr Hills, Dunnellon and High Springs Gaps ............ 135
The Lake Harris and Alachua Lake Cross Valleys .............. 135
The Central Valley ..................................... 136
The Osceola Plain .........................................137
The Caloosahatchee Incline and the DeSoto Plain ................. 139
The Okeechobee Plain ....................................... 142
The Gulf Coastal Lowlands .................................... 142
Terraces of the west side of the peninsula ... ................... .142
Bell Ridge ..............................................148
The Coastal Swamps ...................................... 148
Aeolean Features of the west side of the Peninsual ............... 149
The Gulf Barrier Chain and Lagoons ..........................153
The Proximal or Northern Zone ..................................155
The Northern Highlands east of the Suwannee River .................155
Trail Ridge ..............................................158
Florahome Valley ........................................159
Biography ...................................................161




























vi





ILLUSTRATIONS

Figure
1. Map of Florida showing major transpeninsular
physiographic divisions ....................................... 3
2. Severed boulders of limestone in Everglades near Rock
Reef Pass on Flamingo Highway ................................ 9
3. Contours on exposed surface of oolitic limestone 100 yards
east of Pinelands Trail in Everglades National Park .................. 11
4. Compass direction of open avenues through dwarf
cypress forest on Flamingo Highway ............................ 12
5. Rock Reef in Everglades, a structural lineament,
photograph after Craighead (1964) ............................. 13
6. Air photos showing Shark River lineament ...................... .14
7. Canal across Key Largo showing smooth surface
of marine denudation .................. ................... 16
8. Intricate dissection of coral limestone by solution
from wave splash, Bahia Honda Key ........................... .17
9, Pre-Flandrian solution pit in Key Largo Limestone ................. 19
10. Long Sound Pass, looking eastward ............................ .27
11. Distal growth of a lime bank in Florida Bay ...................... .28
12. Mangrove tree uprooted by erosion on
east side of Blackwater Sound ................................ .29
13. Air photo showing a winding linear group of
individual tree islands strung out along the direction
of water flow, southern Dade County .............. Between 30 and 31
14. Air photo showing short lines of tree islands whose
straightness and parallelism may suggest structural
control, southern Dade County ....... ................... ..... .32
15. Air photo showing line of tree islands in
southern Dade County ..................................... 33
16. Foreshortened sketch showing the relation of lithology
to offshore profiles along the west coast of the
Florida peninsula ....................... ... .............. 35
17. Air photo showing characteristic pattern of
Ten Thousand Islands ....................................... 36
18. The Silver Bluff Scarp on South Bay Shore Drive where
it seems to have been freshened by recent wave erosion
during certain hurricanes ................................... 46
19. West side of Brickell Ave., Miami, showing indurated
wall of old excavation in foreground and new cut in
incoherent oolite behind it .................................. 49
20. Silver Bluff Scarp in distance seen from the
shore of Biscayne Bay ....................................... 50
21. Shore of boat basin off Coral Gables Canal ...................... .51
22. Twenty five foot sailboat washed across some 1000 feet
of what is ordinarily dry land by hurricane Donna in 1960 ........... 53
23. Fossil mangrove roots showing cylindrical holes where
roots rotted out of encasing oolite ............................. .60





24. Fossil mangrove roots in place in cut on west side
of Sunshine State Parkway .................................. 62
25. Cut along sidewalk of N.W. 75th Street, Miami, just
east of St. Mary's Cathedral showing a snarl of fossil
mangrove roots and associated structures in ring-shaped
ridge of relict mangrove island ................. ............... 63
26. Cut in west side of Sunshine State Parkway (Florida
Turnpike) at Honey Hill Road (N.W. 199th St.), showing
ringshaped ridge of relict mangrove island. ....................... .64
27. View eastward along N.W. 75th Street, Miami from a position
near St. Mary's Cathedral. View looks down eastern edge of
ring-shaped ridge formed by relict mangrove island ................ .65
28. Tubular molds of mangrove roots washed out of Miami oolite
from walls of playground in old rock pit in Fort Lauderdale .......... .67
29. Contours on surface of limestone beneath peat in Everglades
alongside Levee 67 about one mile west of U.S. Highway 27,
one foot grid .............................................. 71
30. Contours on surface of limestone beneath peat in Everglades
alongside Levee 67 about one mile west of U.S. Highway 27,
10 foot grid ............................................. 73
31. Geology of the Distal Zone of the Florida Peninsula.
After Schroeder, Klein and Hoy (1958) .......................... 77
32. Isopach map of the Everglades region showing thickness
of peat and some muck areas .................................. 80
33. Profile across the Everglades showing layers of peat and
some marl, rock, and sand sediments .............................81
34. Aerial Photographs of Northeastern Volusia County, Florida,
showing older relict beach ridges truncated by the erosional
scarp of the Pamlico relict oceanic shore line ................... .. .88
35. South bank of South Canal showing section of relict beach
ridge reduced in stature by solution ............................ .96
36. View westward across surface of ground parallel with
South Canal and immediately south of it ....................... .97
37. Air photo of area adjacent to South Canal in Indian River
County about 3 miles southwest of Vero Beach ................... .98
38. Solution pits in Miami Oolite, Fort Lauderdale ................... .100
39. Irregular contact between limestone and insoluble residue
overlyingit in wall of pit used by De Leon Springs as a
town dump ............................................. 101
40. Drainage of Lakes Griffin, Eustis, Harris, Dora and Apopka ......... .105
41. Air Photos of part of the St. Johns River Lake Chain in
Brevard County, Florida ............... ....................106
42. Restoration of relict cape at Orlando showing similarity to
present Cape Kennedy ....................... ..............126
43. Topographic sketch showing the DeSoto Plain as a flat relict
marine shoal in the lee of the distal end of Lake Wales Ridge,
and the Caloosahattchee Incline as the steeper off-shore
end of the shoal ............................ Between -140 and 141
44. Parts of the Manatee Springs and Chiefland 7/2 minute
sheets showing the fluvial appearance of Long Pond and
its tributary valleys ........................................146






PLATES


1-B. Physiographic map of North peninsula Florida ............... Pocket
1-C. Physiographic map of South peninsula Florida ............... Pocket
2. Topographic map of the Miami Ridge showing relic
mangrove islands and the Silver Bluff Beach Ridge ............ Pocket
3-A. Southeastern region of Florida relict shoreline arcs and
Mangrove islands (Northern part) .......................... Pocket
3-B. Southeastern region of Florida relict shoreline arcs and
Mangrove islands (Southern part) .......................... Pocket
4-A. Southern part of the Eastern Valley showing increasing
destruction of relict beach ridges with distance northward
(Northern part) ....................................... Pocket
4-B. Southern part of the Eastern Valley showing increasing
destruction of relict beach ridges with distances northward
(Southern part) ....................................... Pocket
















ACKNOWLEDGEMENTS


Grants numbered GP-1480 and GP-3350 from the National
Science Foundation made to the Geology Department of the Univer-
sity of North Carolina at Chapel Hill defrayed much of the cost of the
investigation described in this bulletin.
I acknowledge with much appreciation the benefit of discussion
with Dr. R. O. Vernon, Mr. W. D. Reves, Mr. J. W. Yon, Jr. and Mr. E.
W. Bishop.
Dr. H. S. Puri cooperated with me in establishing the major
geomorphic divisions of the Florida Peninsula and consulted with me in
the field. His contributions are much appreciated.
Dr. Walter H. Wheeler kindly identified the fossils from South
Canal in Indian River County and appraised their ecologic significance.
I was assisted by my students at the University of North Carolina,
Mr.J. P. May, Mr. E. L. Phillips, Jr., Mr. L. L. Smith and Mr. L. H. Slorp.
I owe much to their work.
Dr. Robert Ginsburg and Dr. J. E. Hoffmeister very kindly gave
me helpful information about the Keys and Florida Bay.





MAJOR GEOMORPHIC DIVISIONS
OF THE FLORIDA PENINSULA

by

WILLIAM A. WHITE



DELINEATION OF GEOMORPHIC FEATURES

Some confusion in the delineation of the physiographic features
of Florida (pl. 1) results from the generally low relief.
In a region of high relief, there is little equivocation in separating
adjacent features. A mountain is recognized as a feature which rises
prominently above its immediate surroundings and its edge is defined
as the break in slope at its base. There is little concern whether this
break in slope forms a level line. Quite generally, it does not. However,\
a region of very low relief, many significant topographic features are
imperceptible to ordinary observation, but are recognized through
knowledge gained from surveying or their effects on flora, drainage,/
culture etc. Under such circumstances, there is a strong tendency to
delineate topographic highs by use of delimiting contour lines. This
tendency is augmented by the fact that such features are ordinarily
defined from a study of topographic maps and it is easy to define them
as being the land above certain specific contours.
Also since the low-lying parts of Florida have been repetitively
below sea level, a number of relict shoreline features have been com-
monly ri :' .nllizcd. These are ordinarily horizontal. Therefore, there
has been a strong tendency to delimit physiographic features by these
relict shorelines and hence by individual key contour lines which
represent the elevations of sea level at the times these relict shoreline
features were made.
To some extent, this tendency is a good one, but it has faults and
they increase with elevation and distance from the present coast. The
higher the shoreline, the older it is and, therefore, the longer it has been
subjected to erosion and sagging because of solution of any limestone
which may underlie it. Farther north, in Georgia, the Carolinas, Vir-
ginia and Maryland, the lower terraces at least have been little de-
formed; they are largely based on insoluble rocks. But the Florida
peninsula is largely founded on limestone which has been differentially
dissolved to allow differential sagging of the overlying surface.





BUREAU OF GEOLOGY


For these reasons, I have avoided the delineation of physiographic
features by single contour lines, and have used natural features as much
as possible. Thus, I have tried to map scarp bases by breaks in slopes
rather than by particular elevations. In certain broad, flat areas of
imperceptible dome-shaped form, such as the Immokalee Rise, I have
been guided more by the extent of the sand and the delimiting zone of
lakes than by a given contour line.

MAJOR GEOMORPHIC DIVISIONS
OF THE FLORIDA PENINSULA
The Florida peninsula can be divided into three physiographic
zones, separated along trans-peninsular lines, oriented about perpen-
dicular to the length of the peninsula (Fig. 1). The Southern or Distal
zone, extends from the southern end of the peninsula to a line that
crosses the peninsula from the general vicinity of Stuart on the east
coast to that of Fort Myers on the west coast. The central or mid-
peninsular zone, extends northward from this line from this last
cross-peninsular line. The northern or proximal zone extends north-
ward to Georgia as far as one which would pass approximately through
the cities of St. Augustine, Palatka, Hawthorne, and Gainesville. Cer-
tain features cross these boundaries from one physiographic zone to
another. Thus, the terraced coastal lowland extends along the west
coast of the peninsula from the northern to the central zone, as does
also the Eastern Valley along the Atlantic side of the peninsula. The
Atlantic Coastal Ridge reaches the entire length of the peninsula from
the Georgia state boundary to Miami, as does also its insular counter-
part the Atlantic Barrier Chain.
The low-lying lands of the southern zone, west of the Atlantic
Ridge, did not reach elevations as high as the Atlantic Ridge on their
eastern rim because they were not exposed to the high energy processes
of the Atlantic shore, which at once carried sand southward from
northern sources to build beaches and fed the corals that built the reefs
of the Keys.
The northern physiographic zone is distinguished by continuous
high ground forming a broad upland which extends eastward to the
Eastern Valley, and westward continuously into the western highlands
of Florida. The central or mid-peninsular zone is characterized by
discontinuous highlands in the form of sub-parallel ridges separated by
broad valleys. The southern or distal zone, is characterized by abroad,
flat, gently sloping and poorly drained plain, fenced on the east by the
Atlantic Ridge.




GEOLOGICAL BULLETIN NO. 51


NORTHERN OR


C)
0 u







0


Figure 1. Map of Florida showing major transpeninsular physio-
graphic divisions


For the most part, the northern zone is high enough to have its
surface above the piezometric surface and is therefore characterized by
many of the features of dry, highland, or "dead-zone" karst, such as
first generation, dry, steep-walled sinks, abandoned spring heads, dry
stream courses, intermittent lakes and dry beds of former broad
shallow lakes which are now prairies.





BUREAU OF GEOLOGY


In general, the ridges of the central or mid-peninsular zone are
above the piezometric surface, but the broad valley floors are below it.
Broad shallow lakes are common on the valley floors and smaller deep
lakes, apparently of rather complex geomorphic history, pock the
ridges. The southern or distal zone, is almost universally below the
piezometric surface and has lakes only in its most northerly part. These
lakes are apparently a carry-over from the central zone and seem to
exist largely because small amounts of sand overlie limestones. Farther
to the south there is no sand. Limestone lies bare or is covered by
post-Floridian peat and lime mud. There are no lakes but broad swamps
dominate the landscape.


THE DISTAL OR SOUTHERN ZONE


MAJOR PECULARITIES OF THE SOUTHERN PART

OF THE FLORIDA PENINSULA

The east coast of the Florida Peninsula changes character at the
latitude of Palm Beach because the upper edge of the continental slope
intersects the litoral zone there. To the north of Palm Beach the
landward edge of the continental slope is farther off shore with
distance northward. To the south of Palm Beach it remains a short and
rather uniform distance off-shore.
This change comes about through a change in the orientation of
the coast line. The outer edge of the Continental Shelf maintains a
smoothly concave regional curve southward from Cape Hatteras (in
North Carolina several hundred miles to the north) all the way to
Miami. In general, the coast line describes a somewhat similar concave
curve of slightly smaller radius that intersects the more gentle curve of
the outer edge of the shelf at Palm Beach. This intersection accounts
for the change in orientation of the coast line at Palm Beach. The curve
of the shelf edge is unbroken and it becomes the curve of the coast line
south of Palm Beach.
This peculiarity of the distal end of the Florida Peninsula is a
major anomaly of the Coastal Plain. It is the only place in the entire
Atlantic-Gulf of Mexico coast of the United States where land extends
all the way to the outer edge of the Continental Shelf. The reason for
this is not wholly clear, but it probably results from the rapid deposi-
tion of carbonates from the tropical water of the Florida current.




GEOLOGICAL BULLETIN NO. 51


Carbonate accumulation is not primarily dependent on mechan-
ical transport agents but on the loci of precipitation. Coral reefs
establish themselves at the outer edges of shoals and grow up to the
surface of the sea forming a sediment trap over the shoal. Calcareous
oolite bores or shoals are precipitated from deep marine water as it rises
to pass over the edge of a shoal. This also tends to form a platform rim
(Newell, Purdie and Imbrie, 1960b). Inside such containing barriers or
even without their protection other biogenic or inorganic precipitation
of carbonates occurs over broad areas indiscriminate of hydraulic or
topographic gradient.
Under such conditions of growth, isolate areas of carbonate
accumulation build up to sea level and out to the edge of the Continen-
tal Shelf. Even where there are no prominent coral reefs, as in the
Bahamas, the outer edges of broad carbonate banks tend to be unusu-
ally steep. Not infrequently they are submarine cliffs.
There are no such abrupt topographic ends to the edges of either
coastal plains or continental shelves where they are dominated by
insoluble plastic sediments. Such submarine surfaces change grade
gently from shelf to shore. At the coast line the gradient shows little
change from coastal plain to continental shelf other than the usual
five-fathom drop from the beach to the sea floor some half mile to mile
off-shore.

Deformation may be involved in the seaward inclination of the
continental shelf. Along a continent's edge, there may be a continuous
isostatic adjustment to the transfer of mass from land to sea. This tends
to keep a hinge line near the coast and tilt both the shelf and the coastal
plain seaward.
Carbonate banks usually are isolate from sources of terrigenous
sediment and have little apparent reason to share such one-way tilting.
Many seem to have subsided great distances but have maintained a
horizontal top at sea level. Perhaps this is an index to rapid sedimentary
growth. They may have been tilted but maintained their tops at sea
level despite the tilting. The asymmetric gravity anomaly in the Ba-
hamas may suggest this.
Rates of carbonate deposition as shown by the geologic section of
the Bahama Banks have been regarded as spectacular but their gross
products are no thicker than insoluble plastic sediments accumulated
on continental shelves in comparable amounts of time. However, the
maintainance of carbonate lowlands and shallow marine banks at
elevations very close to present sea level is not only a matter of rapid




BUREAU OF GEOLOGY


accumulation of carbonate sediment. It is also a matter of equally facile
lowering. Tropical carbonate banks, atols, reefs, and insular and penin-
sular lowlands like Andros Island and south Florida stand almost alone
among areas of late marine sedimentation in having no higher lands
extending significantly above present sea level. Virtually all coastal
plains that border continental oldlands and are made dominantly of
insoluble plastic sediments have flights of broad marine terraces that
attain elevations hundreds of feet above present sea level. Such tropical
carbonate areas as those described above are usually free of broad
terrace flights. Yet the thick Tertiary and Quaternary sections of such
places as the Bahama Banks and south Florida offer good evidence that
they have been in existence for periods comparable to those of the
terraced terrigenous coastal plains of the continents. If their acquisi-
tion of new carbonate sediment is fast enough to maintain them
constantly at sea level, in the past they should have built themselves up
to the several former sea levels reflected in the Terraces of the con-
tinental coastal plains.
Since they rarely show relicts of such former higher surfaces, it
seems reasonable to assume that such surfaces once existed but have
been reduced by denudation or depression. Since extensive remnants
of such relict sea-graded surfaces exist not only on coastal plains built
of insoluble terrigenous sediment, but also in the karst-riddled, !ime-
founded terrain of the central zone of the Florida peninsula, it seems
plausible to assume that the correlative surfaces of the tropical banks
have been lost by subsidence and burial beneath lime deposition rather
than by denudation. Such an assumption is supported by the south-
ward dip of strata from their zone of exposure in the Central Zone to
their increasing burial with distance southward into the Distal Zone.
The Bahama Islands proper are discrepant to this generalization
but they are, I think, a special case. Were they unreduced residuals of
formerly higher broad marine banks like the present Bahama Banks but
built up to former higher-than-present sea levels, they should be
scattered over the surfaces of the present Bahama Banks. Instead they
are all peripheral to those banks and are always located where the
off-shore slope goes precipitately down to abyssal depths, usually to
windward. This assures that deep-water surf is always able to break on
their shores regardless of sea level change, and always in the same place
geographically. The resulting beaches assure a copious supply of sand
which is blown onto the islands' surfaces, where it builds high dunes.
Most of these dunes seem always to have been stabilized by dense
scrubby vegetation that forms an excellent sand trap. And accumulat-
ing under subaerial conditions of agradation such masses of carbonate





GEOLOGICAL BULLETIN NO. 51


sand were probably cemented together progressively as they accumu-
lated. Thus indurated as dune rock they would be constantly subject to
acretion by aeolean deposition but would be invulnerable to wind
erosion.
Evidence that certain Bahaman islands are not remnants of de-
posits made by sea levels much higher than the present one can be had
from Dall (1905) who noted that these islands contain marine fossils up
to an elevation of 15 feet and do not contain any marine fossils at
higher elevations. Also, Newell (1960) says, "Many of the best pre-
served, cemented dunes rest on submerged platforms approximately 3
to 6 meters below sea level." Newell also summarized the age determi-
nations for such Bahaman dune rock. They range from 13,000 to
70,000 years B.P. much younger than the higher terraces of the
Atlantic Coastal Plain, most of which are currently believed to be
Tertiary in age.
With the passage of time and multiple changes of sea level, all parts
of those coastal plains that are dominated by insoluble plastic sedi-
ments have passed through the level of the sea and each in its turn has
located a shore line. These many former shore lines are revealed today
by relict beach ridges, barriers, dunes and other littoral features which
blanket the entire lower part of such coastal plains, as in the Florida
peninsula north of Palm Beach.
In the distal zone of the Florida peninsula, such coastal features
rarely develop, and most of the terrain is built of limey sediment
derived from seawater. This sediment was precipitated in a variety of
ways. And these several kinds of precipitation made a variety of
depositional sedimentary masses that have emerged largely unchanged
to make the present topographic forms. None of these depositional
processes resemble those which distributed the insoluble plastic sedi-
ments of the terrigenous coastal plain to the north. Some of these limey
deposits were accumulations of marine shell, some were oolite, some
were limey muds, and some coral. Few were located strictly by line of
intersection of sea and land. On coasts dominated by insoluble sand,
the temporal succession of beaches causes the shore line to migrate
across an emerging off-shore slope. But in a variety of masses of
limestone which still retain their original depositional form, the loca-
tions of later shorelines at different levels of sea are not arranged in
systematic sequence.
In Pamlico time, when the sea seems to have been about thirty
feet above its present level, most of the Distal Zone of the Florida
peninsula was a shallowly submerged marine bank similar to the
present Bahama Banks. Along its eastern edge, an oolite shoal or bore





BUREAU OF GEOLOGY


formed an elongate bar. As the level of sea dropped from the Pamlico
level, this bar emerged and localized the relict oceanic shore features
now seen in the relict mangrove islands of the Miami Ridge and in the
Silver Bluff shorelines. Protected by this energy-absorbing barrier the
great shoal area emerged under conditions of very low wave energy to
become inland terrane of the distal zone of the peninsula which thus
has no relict features of former high energy shore lines; no relict
beaches, or reefs. After emergence, during Wisconsin time, the Flan-
drian transgression crested at an elevation which allowed sea level to
intersect the seaward front of this bar, determining the present main-
land shore of Biscayne Bay. However, the present level of sea is some 0
to 8 feet lower than the broad expanse of the relict Pamlico marine
bank, which allowed this bank to remain slightly emergent as the
present Everglades.
South of the shoreline scarp that passes north of Lake Okeecho-
bee, there are no obvious relict shorelines in the distal zone of the
Florida peninsula, aside from the Silver Bluff shoreline along the east
side of the Miami Ridge. Apparently the sea receded from these former
marine banks under such low energy conditions that they emerged with
broad, marshy, coastal fringes and left no recognizable shoreline fea-
tures behind them. There is, of course, the possibility that such features
were formed but destroyed by solution during Wisconsin subaerial
emergence.
The topography of the distal end of the Florida peninsula can be
divided into areas like the Immokalee Rise, the Big Cypress, the Miami
Ridge, and the Keys which have not been appreciably affected by
post-Flandrian deposition, and the other areas like the Everglades, and
the littoral areas of Florida Bay and the Gulf Coast where post-Flan-
drian peat, lime mud, shell, or sand has covered and masked the
pre-Flandrian surface.
Generally the noncovered areas are the only ones that show any
perceptible local relief. Thus the Keys and the Miami Ridge have much
more local relief than the peat-covered plains of the Everglades and the
mud-covered flats that surround Florida Bay. To a lesser extent the
Everglades Keys and the Big Cypress are distinguished from their peat
or marl-buried surroundings by demonstrable irregularities of surface.
The areas that have escaped burial beneath post-Flandrian sedi-
ment may be subdivided into those whose surfaces are dominated by
earlier pre-Wisconsin depositional forms as the higher part of the Miami
Ridge, and those dominated by the denudational effects of solution or
marine erosion as in the Coral Keys, the Everglades Keys, and the Big
Cypress.





GEOLOGICAL BULLETIN NO. 51


Figure 2. Severed boulders of limestone in Everglades near Rock
Reef Pass on Flamingo Highway



The drainage of the distal zone of the Florida peninsula shows
little consequence to relict coastal features where post-Flandrian
deposits make its surface. Because the peat and lime mud of such
deposits are the result of swampy conditions, they have built up the
ground surface and allowed the water to braid its flow over all parts of
the land surface. Also braided drainage has developed in post-Flandrian
time on the swampy surfaces of bare pre-Wisconsin limestones as in the
Big Cypress and the Everglades Keys. These areas seem to have devel-
oped ragged karstic surfaces of small local relief in glacial times of low
sea level. Now solution is planing them down to a sub-aerial water table.





BUREAU OF GEOLOGY


This present surface planation is tested by little natural bridges
and rock pedestals a foot or two high, and by solution-riddled, severed
boulders of comparable stature that lie loose upon the bed rock
surfaces, figure 2. In such places small structurally-controlled subse-
quent features are still evident. They are seen in the structural line-
aments, shown on the microtopographic map of an area 10 feet square
at Pinelands Trail in Everglades National Park, figure 3. On a larger scale
they are shown by the infra-red aerial photographs of an area near the
place where the old Ingram Highway intersected the present Flamingo
Road, (Florida State Highway 27). These color photographs which
show green as red reveal prominent lineation in the exposed limestone.
This lineation is shown by its control of the places where pine trees
have been able to grow. Most of them seem to be rooted in small sinks
that were filled with organic debris by smaller plants that occupied the
sinks earlier. The sinks which are revealed by the pine trees seem to be
located along structurally controlled lineaments. In the photograph,
the pine trees are seen as pink dots which are arranged in parallel or
geometrically similar rows.
Farther west where the water table is at the surface of the gorund,
dwarf cypress trees are rooted in similar small sinks and are also aligned
in subparallel rows. Looking through the dwarf cypress forest, such
alignment is frequently seen resembling the rows of trees in an orchard.
Figure 4 shows the orientation of a number of sightings along such rows
of cypress trees.
Occasionally, larger structurally-controlled features are preserved
from the karstic dissection of pre-Flandrian times of lower sea level.
Rock Reef in the Everglades Keys, figure 5, is one of these. It is an
assemblage of structural lineaments that stand a little higher than the
surrounding land because they have resisted solution better.
Somewhat similar is the major structural lineament in the Ever-
glades Sloughs that located the Shark River, figure 6, and confined it to
a remarkably straight course as it passes through the plexus of asso-
ciated streams that share its job of draining the Everglades to the Gulf
of Mexico. Unlike the structures that made Rock Reef, the one that
made the Shark River lineament seems to have been an avenue of easy
movement for ground water. Instead of making a ridge like Rock Reef,
it made a linear depression to which the Shark River became conse-
quent as the Flandrian transgression crested and the water table rose to
the surface of the ground.
The Shark River lineament is a major one. It is long and straight.
On the assembled photo-index sheets of the distal end of the Florida
peninsula, it can be traced from the Gulf coast immediately north of





GEOLOGICAL BULLETIN NO. 51


0 I 2 3 4 5 Feet
Approx.Scale


Figure 3. Contours on exposed surface of oolitic limestone 100
yards east of Pinelands Trail in Everglades National Park





BUREAU OF GEOLOGY


N
























Figure 4. Compass direction of open avenues through dwarf cypress
forest on Flamingo Highway

Cape Sable to the Atlantic Coastal Ridge near Fort Lauderdale. It is one
of the major structural lineaments along which the several contempora-
neous Pleistocene formations are juxtaposed. (df., the section of this
report called the Everglades Trough). It is parallel with the trend of the
Low Coral Keys and the Oolite Keys, with the postulated fault that
bounds the Pourtales Scarp southeast of the Keys (Jordan, Malloy, and
Kofoed, 1964), and with the Caloosahattchee-Okeechobee fault-
founded lineament that bounds the Distal zone of the Florida penin-
sula at the north (Tanner, 1966).












,A &


A?. :r


Figure 5. Rock Reef in Everglades, a structural lineament, photograph after Craighead (1964)


* I,






S- V.



rNt


i>1Wro


IFq


lVP.


*" -'


4L-
""if '^r^^ ^'

-^^ "^^^.i c;
wI; -. .^ r .^aff


A..i'f

II


,' ~, ,-.-


Figure 6. Air photos showing Shark River lineament


L
4
a


, '




GEOLOGICAL BULLETIN NO. 51


Beaches are made where waves spend their energy on bottoms
that can produce sand. Such places are so common that oceanic
shorelines rarely fail to be dominated by beaches.
There is a southward drift of sand along the Atlantic Coast which
extends in diminishing volume as far south as Cape Florida (Key
Biscayne), but south of Palm Beach there is little source of sand other
than comminuted shell, and the beach is so close to the brink of deep
water at the upper edge of the continental slope that sand is probably
carried into the abyssal depths of the Florida Straits and lost to the
beach. The supply of sand gives out completely at Cape Florida and
beyond it there are no beaches. Somewhat similarly on the west coast
of the peninsula the supply of sand for making beaches gives out at
Cape Romano and the Ten Thousand Islands. From Cape Florida to
Cape Romano the dearth of sand prevents this strongest of coast-form-
ing processes from working, and between these two capes lies one of
the few parts of the Coastal Plain where oceanic shores are not
dominated by beaches.

In the absence of the strong, the weak are able to express them-
selves, so the character of the oceanic shoreline has been determined by
various weaker factors such as relict coral reefs and oolite shoals, the
precipitation of lime mud and the growth of mangroves and vermetid
gastropods. Thus a variety of low energy coasts have developed along
the southern and southwestern shores of the Florida Peninsula, none of
which would have been possible had the usual sand been present to be
thrown up in beaches by the waves.



THE FLORIDA KEYS

THE HIGH CORAL KEYS

The High Coral Keys seem to have been an active coral reef at the
time the Miami Ridge was an active oolite shoal and possibly also while
it was emerging to form mangrove islands. The present surface of the
High Coral Keys is a denuded one from which the original surface of the
coral reef has been completely removed. In the highest parts of the
High Coral Keys (mostly on Key Largo east of the place where U.S.
Highway No. 1 enters the Coral Keys from the mainland and on
Windley Key near the quarry) there seems to be no evidence of
resubmergence since the original emergence. The surface has some
considerable local relief and occasionally shows the ragged irregular




BUREAU OF GEOLOGY


Figure 7. Canal across Key Largo showing smooth surface of marine denudation

surface of micro karst. Also there are local accumulations of residual
soil. All these features suggest that these higher parts of the Keys have
remained under conditions of subaerial exposure for the greatest part
of the 100,000 years (Broecker and Thurber, 1965) since the coral of
the reef was formed. There are no topographic maps of the High Coral
Keys but there are two places that are said to reach elevations of 18
feet. Both of these are in these higher, rougher, never resubmerged
places, one on the eastern part of Key Largo, the other at the quarry on
Windley Key.
The remainder of the High Coral Keys have a lower, smoother
surface which seems to have been made by marine denudation. Near
the outer and inner edges of the relict coral reef this surface slopes
gently down toward the present shore (Fig. 7) where it is being cut back





GEOLOGICAL BULLETIN NO. 51


Figure 8. Intricate dissection of coral limestone by solution from
wave splash, Bahia Honda Key
by solution from wave splash (Fig. 8) in the present cycle of shoreline
denudation. In this process a recent surface of the same kind is being
formed immediately offshore. The shore zone that is repetitively wet
by wave splash is intimately dissected to make an extremely ragged,
irregular surface of bare coral rock honeycombed with solution holes.
Most of these are a few inches to a foot or so wide and not greatly
different in depth.
The origin of this sort of surface has been discussed by several
writers. Agassiz (1896), and Ginsburg (1953) have dealt with the
Florida occurrence. There is general agreement that it has been made
by solution but opinion differs as to the immediate mechanism;
whether it be done by boring organisms or by physical-chemical means
without the assistance of living organisms. Ginsburg (1953) made a





BUREAU OF GEOLOGY


good case for the influence of boring animals. But in 1957, Kaye found
that limestone exposed to splashing (bursting bubbles) acid dissolved
much more rapidly than when immersed in the same acid. In the light
of his findings I am inclined to believe that wave splash is the dominant
mechanism that facilitates solution along tropical limestone shores.
These ragged, differentially dissolved surfaces are found only on shores
of some considerable wave energy. Deposition tends to replace them on
low energy shores.
On high energy shores the solution seems to be confined to the
zone that is commonly wet by wave splash for the ragged surface
doesn't persist below low water level. Instead, a broad, flat, bed-rock
surface reaches long distances offshore. This seems to be a newly
formed surface leveled at depths of a few inches to a few feet by the
shoreward retreat of the ragged zone of active solution above low water
level. At the seaward edge of the shore zone of active solution pedestals
form, and severed boulders lie about on the landward edge of the newly
beveled zone. Much of this newly beveled bed rock surface is exposed
under shallow water but probing with a steel rod showed it persisting to
distances several hundred yards off shore beneath a few inches to a foot
or two of unconsolidated sediment.
This newly cut, sea level-controlled, post-Flandrian bedrock sur-
face is the morphologic counterpart of the surface of the lower, flatter,
smoother part of the High Coral Keys. This suggests that the higher,
older surface was cut at some earlier Pleistocene time when sea level
was about 10 feet higher than present.
The higher, rougher, more soil-covered parts of the High Coral
Keys, as in the eastern part of Key Largo and near the old quarry on
Windley Key, would have been islands in this sea that were not bitten
away by the shoreline solution that beveled the lower, smoother,
flatter parts.
The level of sea that did this beveling of the High Coral Keys seems
to have been the cresting of a transgression rather than an interval of
stability during a regression. Moreover, the span of time between the
regression of the sea from its Pamlico level (when the Key Largo Coral
Reef seems to have been built) and its rise to the 10 foot level that
beveled most of the High Coral Keys seems to have been much longer
than the later span of time since the sea regressed from that 10 foot
level to leave the lower, smoother parts of the High Coral Keys
exposed. This assumption follows from the presence of an appreciable
accumulation of residual soil on the higher parts of the High Coral Keys
and a virtual absence of residual soil from the lower, smoother, wave-
beveled parts.





GEOLOGICAL BULLETIN NO. 51


Figure 9. Pre-Flandrian solution pit in Key Largo Limestone


It is this brown residual soil that attests the transgression that
culminated in the 10 foot sea level stand. The walls of two widely
separate cuts in the wave-beveled part of the High Coral Keys show old
solution pits filled with such brown soil and fragments of limestone.
Apparently these pits were dissolved out by fresh ground water before
sea level rose to the 10 foot level at which it beveled the surface of the
lower, smoother parts of the High Coral Keys.
Such wave-beveled, soil-filled solution pits can be seen in the wall
of the canal at Seven Acre Estates on the north shore of Key Largo 3.4
miles from its southwestern end (Fig. 9). They may also be seen in the
eastern wall of the Key Largo Waterway (Kids Kut) south of U.S.
Highway No. 1.


THE LOW CORAL KEYS AND THE OOLITE KEYS

Between Upper and Lower Matecumbe Keys is the boundary
between the High Coral Keys described above, and a lower surface
which extends all the way to the southwestern end of the Florida Keys.
This surface has about half the elevation of the lower, flatter, beveled
parts of the High Coral Keys. Its eastern part from lower Matecumbe





BUREAU OF GEOLOGY


Key to Newfound Harbor Keys is part of the same relict, emerged, coral
reef of which the High Coral Keys are made. On the map it is seen as the
western distal part of the same long, narrow, smoothly-curved archipel-
ago of which the High Coral Keys form the eastern, proximal part. All
these coral keys, both high and low, are elongate in the direction of the
length of this arc parallel with the general trend of the coastline. Their
lower, western part is the Low Coral Keys.
To the west and north of the Low Coral Keys lie the Oolite Keys.
These share the low, eroded surface of the Low Coral Keys and in gross
plan as a group of islands, they continue the westward curving coast
line of the Coral Keys. However, this western extension of the curving
archipelago is set back northward a few miles forming an abrupt break
in the trend of the coast line. Also the Oolite Keys overlap the western
end of the Low Coral Keys by some 15 miles extending in behind them
to the northeast. The general trend of the Oolite Keys as a group is
east-west, sharing the same direction of elongation as the Coral Keys,
but individually the Oolite Keys tend to be elongate perpendicular to
this direction, usually a little west of north.
The surface of the Low Coral Keys closely resembles that of the
lower, flatter parts of the High Coral Keys and gives every indication of
having been formed in the same way; that is, beveled by solution along
the shore line of the sea. It is smooth and flat in the center of an island
and near the shore it slopes gently downward. Like the wave beveled
parts of the High Coral Keys it bears little if any residual soil. No
subaerially made solution pits were observed but there are few cuts that
might be expected to reveal them.
The surface of the Low Coral Keys seems to have been beveled by
a sea level some four or five feet higher than the present level of sea. But
in the absence of relict subaerially made features extending below this
surface it is not clear whether the sea rose to this level from a lower
stand or dropped to it directly from the higher stand that beveled the
lower parts of the High Coral Keys.
In plan the Oolite Keys are a mirror image of the Mianii Ridge in
that they relate to the southwestern end of the Coral Keys (the Pamlico
coral reef of the Key Largo coral limestone) the same way the Miami
Ridge relates to its northeastern end. Both the Oolite Keys and the
Miami Ridge are relict oolite shoals or bores. Both are set back from the
arc of curvature of the seaward front of the Coral Keys. Both overlap an
end of the relict reef extending in behind it and gradually losing stature
as they pass into its lee. The Miami Ridge extends southwestward
behind the northeastern end of the relict reef and loses stature as it does
so until it loses its identity a short distance southwest of Homestead




GEOLOGICAL BULLETIN NO. 51


and Florida City. Similarly, the Oolite Keys extend northeastward
behind the southwestern end of the old coral reef and become more
sporadic and sparse in distribution until they disappear entirely beyond
East Bahia Honda Key. Both the Miami Ridge and the Oolite Keys have
coast-perpendicular avenues running through them; the transverse
glades of the Miami Ridge and the channels of the Oolite Keys.
These similarities leave little doubt that these two relict oolite
shoals or bores were made in the same way at opposite ends of the coral
reef that now forms the Coral Keys, but their dissimilarity in stature
raises the question whether they were formed at the same former time
of high sea level or at different sea levels at different times.
The relict oolite shoal that forms the Miami Ridge has stature
roughly commensurate with that of the higher part of the High Coral
Keys. It seems most plausible to assume they both were made during
Pamlico time. The evidence for a Pamlico high sea level is well estab-
lished and its level was very close to the level of sea at which these two
relict features would have been formed.
The Oolite Keys on the other hand have much lower maximal
elevations the same as those of the Low Coral Keys. Hence, it would
seem possible that they could have been made as an oolite shoal at
either of the other two levels of sea recorded in the smooth, beveled
surfaces of the Low Coral Keys (3-4 feet) and the High Coral Keys
(some 10 feet). But two things suggest that the Oolite Keys were made
at the higher Pamlico level of sea.
The age of the oolite of the Oolite Keys is the same as that of the
coral of the High Coral Keys. For oolite from Key West Broecker and
Thurber (1965) got uranium series ages of 90+9 thousand years and
120+10 thousand years. For coral rock from Windley Key they got an
age of 95+9 thousand years and for coral rock from Key Largo they got
ages of 130+20, 130+15, and 140+15 thousand years. Two other older
ages from Key Largo they considered unreliable.

Although parts of the Coral Keys have been reduced by wave
attack twice in post-Pamlico time they seem never to have been
resubmerged to a depth great enough to get another growth of coral.
Hence, all the coral rock of the Key Largo formation should be Pamlico
age or older. And, since the oolite of the Oolite Keys has the same age,
it too should have been made during the Pamlico high level of sea.
However, the surface of the Oolite Keys shares the low elevation
of the Low Coral Keys which raises the question of whether it was
lowered to this level in the same period of shoreline solution that
beveled the Low Coral Keys or was a shallowly submerged oolite bank




BUREAU OF GEOLOGY


in the Pamlico Sea. Perhaps the internal structure of the oolite may
help answer this question. The oolite of the Miami Ridge is shown to be
an unreduced Pamlico shoal by its ring-shaped ridges that have maximal
elevations comensurate with those of the High Coral Keys. These ridges
contain fossils of mangrove roots that grew in the oolite as it emerged
from the Pamlico Sea. The oolite of the Oolite Keys shows few if any
fossil mangrove roots. This suggests that the shoreline erosion which
beveled the Low Coral Keys also removed the upper part of any relict
mangrove islands that formed as this distal oolite shoal emerged from
the falling surface of the Pamlico Sea. The fossil mangrove roots would
have been contained in this upper part that was removed. Had the
oolite shoal formed at one of the lower sea levels that beveled the Keys,
the fossil mangrove roots should still remain.
Another confusing matter is the difference between the transverse
Glades of the Miami Ridge which are wholly emergent and the trans-
verse channels which are then submerged counterpart in the Oolite
Keys. On first thought this suggests down-warping of the Oolite Keys at
the southwestern end of the archipelago while the Miami Ridge on the
east side of the peninsula remained stable. However, this does not seem
to be the case. Instead this discrepancy seems better explained by the
presence of water on both sides of the Oolite Keys which let tide rips
erode the transverse channels down to lower levels as sea level fell. In
the case of the Miami Ridge the transverse glades seem to have been
similarly eroded down by tide rips to the level at which the floor of the
Everglades emerged from the sea. This emergence stopped the tidal
exchange of water and the former transverse channels became the
present transverse glades.


FLORIDA BAY

The history of Florida Bay is difficult to decipher. Its general
outline suggests a bell-mouthed estuary widening westward from a
headwater area at the structure where it passes in to the south end of
Biscayne Bay. But there is little to suggest that it ever carried the
drainage of any appreciable area outside its present limits despite the
repetitive pattern of westward turning peninsular drainage as seen in
the Caloosahatchee River and the Everglades Sloughs.
More probable is an origin as a lagoon. However, this is compli-
cated. Lagoons that border coastal plains are usually thought of as
creations of the Flandrian transgression; separated from the ocean
proper by barriers built since the transgression crested essentially at




GEOLOGICAL BULLETIN NO. 51


present sea level. But, Florida Bay is enclosed by the Coral Keys, a
pre-Wisconsin coral reef, and the Oolite Keys, an emerged oolite bore.
Furthermore, three different sea levels seem to have been involved in
making the present subaerial surface of this containing barrier. A high
one beneath which the northeastern part of Key Largo grew up as a reef
to elevations greater than those found it its present irregular karstic
surface, some 18 feet; a lower and later one at which waves planed the
western end of the High Coral Keys to an elevation of some 10 feet, and
a still lower and later one during which the Low Coral Keys were planed
to their present level of some four feet elevation. The Oolite Keys
would seem to have been formed at one of the higher of these sea levels
since some six feet is the optimum depth for the top of an oolite bore
(Newell 1960). But their equality in elevation with the Low Coral Keys
suggests that both Oolite and Low Coral Keys were planed at the same
time by a sea level somewhat lower than that at which either was
deposited.
Explanation of Florida Bay compatible with these observations
demands either that it has been eroded out of a wave-planed surface or
that it is a twice-reinundated relict lagoon from an interglacial high sea
level. My tendency is to lend some credence to both possibilities,
suggesting that an interglacial lagoon has been reinundated after suffer-
ing some reduction by solution during glacial low sea levels.
Such reduction by solution would be compatible with other
major features of the distal part of the peninsula. The drainage of the
Everglades is presently confined by the Miami Ridge, and it would seem
plausible that during somewhat lower sea levels the Florida Keys
should similarly have confined the drainage of the area now occupied
by Florida Bay.
Of course, such confinement would be insecure during sea levels
much lower than present because the steep off-shore slope beyond the
Keys would promote drainage escape by underground solution avenues
or solution-deepened channels between the Keys. Precedent for this
last is seen in the 100 feet of fill in the channel of the New River
(Parker, Ferguson, Love and others, 1955). Somewhat lesser depths of
fill were found in the North New River in explorations made for the
tunnel that takes U.S. Highway 1 under it in Fort Lauderdale.
The buried topography of the bedrock (oolite) surface beneath
the post-Flandrian lime mud of Florida Bay suggests, a broad low
divide extending westward through the center of the bay from its
eastern end and curving southward between two broad bedrock swales
that would seem to have drained through one of the inlets near the west
end of the High Coral Keys.




BUREAU OF GEOLOGY


THE ISLANDS AND SHOALS OF FLORIDA BAY

The islands and shallow banks of Florida Bay are quite discrete
from its essential containing bounds and its oolite floor which are
pre-Flandrian in origin. The islands and banks are made of post-Flan-
drian lime mud and their surfaces usually lie within a foot above or
below normal water level. The most western of these banks are sandy
and extend southeastward from East Cape (the southeasternmost of
the three component capes of Cape Sable.) They face deeper, open
water of the Gulf of Mexico on their west side. Perhaps for this reason
these western banks are somewhat broader and sprawling in plan. But
all the other banks to the east of these are made of mud and form a
plexus of long narrow, intersecting Thalassia-covered shoals and man-
grove-covered islands.
According to Scholl (1966) the mud is some 89 to 90 per cent
calcareous and made in the water of the bay or in marine water nearby.
The plan of these elongate mud banks is difficult to explain. I
think the attenuate form results from distribution of sediment by a
plexus of currents whose present pattern of flow is largely determined
by the deflection effected by the banks. Probably this plexus of banks
acquires a denser distribution as cumulative sediment is produced with
the passing of post-Flandrian time. The currents of this part of Florida
Bay are weak and complex in pattern of flow. Gorsline (1963) calcu-
lated slow rotational currents in some of the "lakes" between banks
and islands. Regardless of what their pattern of flow may originally
have been at the crest of the Flandrian transgression when Florida Bay
may have been a continuous body of open water, it is now influenced
by the arrangement of the banks. The banks in turn seem to have
accumulated from deposition of the limey mud distributed by these
currents. In effect the banks and the currents seem to have evolved
together, mutually affecting each other.
Not infrequently narrow moats of deeper water lie close along the
edges of the islands. Usually these are some six to eight feet wide and
two to three feet deep. They lie close along the shores of mangrove
islands, separating them from thalassia-covered banks, where the water
is commonly less than a foot deep. In these moats perceptible currents
can be seen on most occasions. Such moats are frequently overhung by
the branches of mangrove trees that cover the low islands the moats
encircle. The water of the moats is deep enough to float mangrove seeds
in the erect position and carry them down-current. I think this helps to
distribute the mangrove growth along the drift of the current. In turn
the mangrove probably serves as a sediment trap for lime mud carried




GEOLOGICAL BULLETIN NO. 51


by the same current after winds have disturbed the bottom and
muddied the water.
Seeds of the red mangrove (rhizphora) are peculiarly designed to
be carried by currents rather than by winds. When ripe seeds were
picked from the tree and dropped into the water of the inlet between
Blackwater Sound and Little Blackwater Sound, they first floated in a
horizontal position with their length parallel with the surface of the
water. But after two or three minutes of immersion they changed their
position and began to float with their length perpendicular to the
surface of the water.
At first when these seeds were floating in a horizontal position
they were blown across the water surface by the wind gusts of the
moment. But after they changed position and began to float in their
more permanent, vertical position they moved with the current rather
than the wind. Floating in this vertical position they resemble float
bottles. Most of their length is submerged and only a small share of it is
above water. This preponderant exposure to water rather than air
allows the water currents rather than the wind to dominate their
direction of travel. Seeds picked from mangrove trees on the west side
of Long Sound Pass (between Long Sound and Little Blackwater
Sound) floated across the inlet and lodged in shallow water on its
eastern side in a place where many mangrove seedlings were beginning
to grow despite considerable evidence of shoreline erosion to depths of
six inches to a foot or so.
A somewhat similar situation seems to have shaped the tree
islands of the Everglades. The plan of these is characteristically tear-
drop shaped, with the blunter end facing up-current, and the narrow
tail pointing down-current. The tree islands seem to have acquired this
tear-drop plan by splitting the flow of the water which used to drift
over the surface of the Everglades before the present drainage works
lowered the water level and dismembered the natural drainage. The tree
islands vary much in ratio of width to length, and grade into linear
sub-parallel distributions of different kinds of vegetation which gave
the Everglades a striated appearance on early aerial photographs (Davis,
1943). These attenuate forms of the vegetal distributions of the Ever-
glades have a much more uniform orientation than the shallow banks
and islands of Florida Bay. This is because they are the product of a
uniformly oriented drift of fresh water which flows down a regional
topographic slope. The currents of Florida Bay obey no such uniform
discipline but are variously affected by winds, tides, and possibly
barometric pressure and water density. The result is that they devel-
oped a parcelled and variable pattern of flow directions as the forces




BUREAU OF GEOLOGY


which drove them changed direction. The result of the intersection of
these variously oriented currents produced an arrangement of sediment
which shows little order other than a network of attenuate, intersecting
shallow banks and low islands. Once established, this network of
deflecting barriers has tended to promote circuitous, orbital currents in
each partially or completely enclosed "lake". It is my opinion that
these currents tend to repair any breaks in the continuity of the linear
banks by drifting mangrove seedlings and lime mud into the breach.
Figure 10 shows such a breach at Long Sound Pass between Little
Blackwater Sound and Long Sound. At the time the picture was taken,
a perceptible current was flowing across this breach from west to east in
agreement with the wind direction at the time. As described above,
mangrove seeds dropped into the water on the western side of the
breach floated with the current across the breach toward its eastern
side. The end of the opposing septum of land on the eastern side of the
breach was undercut by the current or perhaps more plausibly by the
waves made by the same wind that drove the current. Its edge was
sharply truncated, and a dense growth of mangrove seedlings covered
it. These observations support the idea that the distal ends of such septa
of lands are points of geomorphic activity, both erosional and deposi-
tional, and I feel that the intersecting network of such attenuate banks
maintains and modifies itself by such distal activity. Successive concen-
tric acretions of sediment at the distal end of an island in Florida Bay
can be seen on the air photo shown here as figure 11.
Quite generally capes, points of land, distal ends of shoals, beach
groins, and similar attenuate protuberances deflect currents that other-
wise would flow past them. Thus long-shore currents approaching such
protuberances from either direction are deflected in the same offshore
direction. In high energy environments the sedimentary efforts of such
currents are modified or negated by wave erosion but in quieter waters
they seem to be able to extend the protuberances that beget them by
cumulative deposition of current-borne sediment at the distal ends of
the coastal protuberances. In Florida Bay the low energy of the quiet
water assures that such sediment will be mud rather than sand.
Probably there is an alternation between brief occasions, of ero-
sion during storms and long periods of sediment accrual during quieter
weather. During the high energy conditions of storms, waves in the
"lakes" between the banks scour the bottoms of the "lakes" and erode
the sides of the banks. Figure 12 shows the eroded edge of such a bank
on the east side of Blackwater Sound. Note the undermined mangrove
tree overturned in water 5 feet deep. The depth of scour in the "lakes"
is generally limited by the upper surface of the Miami oolite which


























- p-


Figure 10. Long Sound Pass, looking eastward





28 BUREAU OF GEOLOGY


Figure 11. Distal growth of a lime bank in Florida Bay




GEOLOGICAL BULLETIN NO. 51


... "Y4; ,,



.









k-,,.









Figure 12. Mangrove tree uprooted by erosion on east side of Black-
water Sound



everywhere underlies the water of Florida Bay at shallow depths,
usually between 5 and 9 feet. Apparently the surface of the oolite was
cemented during subaerial exposure in Wisconsin time and it now
forms a resistant base to wave scour. Thus the storm waves stir up the
post-Flandrian sediment but leave the cemented oolite as a stable floor
that tends to be scoured clean. The post-Flandrian sediment is almost
wholly mud and, once disturbed by erosion, it lacks the coarse com-
ponent necessary to make lag gravels and build sand bars. Being almost
wholly of particle sizes that can be held in suspension by slowly moving
water, much of it stays in suspension until currents carry it to vegetal
sediment traps such as the attenuate ones described above.





BUREAU OF GEOLOGY


This process would promote the development of two discrete
environments, one of erosion down to bed rock (oolite) in the "lakes",
the other of deposition up to water level on the attenuate shoals. And
the boundaries between these two environments should be fairly sharp
because wave erosion undermining the edges of the depositional areas
would move only fine mud that could not be distributed locally in
gradational bars but would remain in suspension while it moved
through the same routes to the active vegetal sediment traps.
The marine grass thalassia (usually called turtle grass in south
Florida) also seems to be an important contributor to the system of
vegetal sediment traps. It covers most of the shallow banks that are not
dominated by mangrove. It makes a mat of subaqueous vegetation far
denser and finer textured than that afforded by mangrove. Further-
more it has been shown (Dr. W. W. Hay personal communication) that
it prefers to grow in places where currents are swiftest. The resulting
tendency for it to make a dense mat of leaves where currents sweep the
bottom should provide good sediment traps where currents carry
sediment most voluminously. Plausibly, banks that have been shoaled
or distally extended with sediment trapped by thalassia may later be
colonized by mangrove as they become too shallow to support thallas-
sia any longer. Moreover the mortality of individual leaves of thalassia
seems to be high because many small, sessile, carbonate-secreting
organisms attach themselves to the leaves. These probably make a
considerable contribution to the accumulated sediment on which the
thalassia grows.
To repeat, in summary: The post-Flandrian sediment of Florida
Bay is dominantly fine mud which is either protected by vegetation
(thalassia or mangrove) or eroded by storm waves. Much of that eroded
remains in suspension until currents carry it to vegetal sediment traps
whose shape and location are determined by these same currents
because the vegetation that forms the sediment trap is localized by the
currents that deliver the sediment. The thalassia grows best in currents
and the currents carry the mangrove seeds to the places where they root
themselves.

DRAINAGE OF THE AREA ADJACENT
TO THE NORTH SHORE OF FLORIDA BAY


In southern Dade County, between Homestead at the north and
Florida Bay and Barnes Sound at the south, the parallel pattern of
drainage on the distal slope of the peninsula is characteristic of agrada-






















































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GEOLOGICAL BULLETIN NO. 51


tion. A sheet of water covers it all, and the darker zones seen in air
photos are chains of higher vegetation rather than stream channels. The
little spermatazoon-shaped patches of vegetation with tails pointing
down slope are tree islands and in many places they can be seen merging
in chains to evolve ultimately up or down-stream into more continuous
strings of vegetation that become the dark lines seen on the air photos.
The origin of these tree islands is not wholly clear. Some of them
may be established in places where pre-Wisconsin solution lowered the
surface of the oolite. If this be true it would seem necessary that the
coastward drift of shallow ground water had been channeled through a
series of such small solution openings and had made connecting open-
ings between the original holes to account for their being connected in
coast-perpendicular chains.
Another possibility might be that the higher vegetation of tree
islands deflected the surface water drift to control the distribution of
floating vegetal matter including seed. Individual tree islands would be
consolidated into chains by lodgement of such debris.
Various arrangements of tree islands exist. Figure 13 shows a
winding linear group of individual tree islands strung out along the
direction of water flow. They seem to be approaching integration and
have achieved it at their downstream end where they become a con-
tinuous zone of trees. Such a wandering line of tree islands makes little
suggestion of structural control. Figure 14 however, shows several
short lines of tree islands that are notably straight and parallel. These
might be easier to interpret as structurally controlled were it not for
their neatly coast-perpendicular orientation. Figure 15 shows aline of
tree islands that is straight in its northern part and well integrated.
Apparently the water flows along the length of the line of tree islands.
In the southern half of the line the tree islands are less well integrated
and have a different orientation which seems to be at an angle with the
general direction of water flow. Here the individual tree islands are
arranged en echelon with their tails pointing in the same direction as
the better integrated northern half of the line. However, these en
echelon islands seem to be growing together because of their joint
effect of deflecting some of the water which approaches their up-
stream flank. Apparently the deflected water promotes the vegetal
growth that integrates the individual islands into chains.
Price (1967) sees a genetic influence of earlier instances such lines
of higher vegetation (his "rill divides") on the elongate shoals and
islands of Florida Bay to the south. Certainly they extend southward
short distances into the Bay; possibly because they offer greater
resistance to shoreline erosion than do the less vegetated areas of lime





BUREAU OF GEOLOGY


MWm I J& X *A t J A 1%. '-771'-, -
Figure 14. Air photo showing short lines of tree islands whose straight-
ness and parallelism may suggest structural control, south-
ern Dade County.
mud between them. However, most of these small peninsulas are
truncated a short distance offshore and the few that ramify into the
reticulate system of lime shoals and islands loose their coast-parallel
orientation and partake the curvilinear form of the shoals and islands of
the Bay. Mostly they adopt a coast-parallel elongation.
Craighead (1964) has described storm levees along the north shore
of Florida Bay. These have dominantly coast-parallel (east-west) elon-
gation and seem to mark the northern edge of the direct effects of
Florida Bay. The sediment transporting capacity of Florida Bay lessens
landward and finally the coast-parallel storm levee seems to end the
direct influence of the bay in the same place that it effaces the features
of the fresh water drainage.






GEOLOGICAL BULLETIN NO. 51


Figure 15. Air photo showing line of tree islands in southern Dade
County


THE LOWER WEST COAST OF THE PENINSULA

The differences of the several parts of the western and southern
coasts of the peninsula are largely a result of differences in the original




BUREAU OF GEOLOGY


materials encountered by the waves as they attacked the land at the
crest of the Flandrian transgression.

It is notable that the sandy coasts (such as those of the west coast
beach resorts between Anclote Key at the north and Cape Romano at
the south) are at once steep in offshore profile and geographically
protuberant in plan. They make a broad, coastal salient between
equally broad reentrants to north and south. The salient has ubiquitous
sand barriers separated from the mainland by lagoons. By contrast the
limestone-floored coastal reentrants have very gentle offshore profiles,
little sand and either degenerate barriers, as south of Cape Romano or
none at all as in Suwannee Bight north of Anclote Key.
Figure 16 shows this relation between profile and kind of stuff
that makes the sea bottom. In the sandy, protuberant part of the coast
between Anclote and Marko Keys there are many relict barrier bars and
beach ridges to landward and the five-fathom isobath is rarely more
than half mile offshore from the oceanic beach on the barrier. By
contrast, in the sand-starved coastal reentrants to north and south,
relict shoreline features are absent or obscure, the coastline is indeter-
minate, gradational, and marshy, and the five-fathom isobath lies 20 to
30 miles offshore. For the most part the five-fathom isobath tends to
be fairly straight across the three sections of coast, being close to the
protuberant sandy section, and remote from the reentrant sand-free
sections. This suggests that it marks a contour on a part of the
pre-Flandrian subaerial surface which has not been appreciably
changed by marine processes of erosion or deposition other than having
a barrier thrown up on its landward side where it traverses sandy
bottom. The barrier appears immediately landward (shoalward) from
this line because five-fathoms is a depth close to the nearly ubiquitous
maximum for depth of wave scour on oceanic shores. This straightness
of the five-fathom isobath along the west coast of the Florida peninsula
suggests that the protuberant, steep-profiled, high-energy, sand-domi-
nated section of the coast has been built out to the five-fathom line
rather than the reentrant, gentle-profiled, low-energy, marshy coasts
being cut back from it. The high wave energy could more plausibly
throw up sand at wave base to build a barrier island than the slow
dissipation of wave energy through a 20 or 30 mile zone could account
for the gradual off-shore slope of this zone by 20 or 30 miles of
shoreline regression from wave erosion. Actually, this latter evolution
seems impossible in the face of the existence of subaerially produced
peat on the sea bottom offshore from the marshy southwestern coast
of the peninsula (Spackman and others, 1964 Shier 1969) because this
peat would have been removed by wave erosion had the submarine

















400-
Scale for cross sections
FEET 200
100-
15 30 45 60
MILES


sand-






limestone


CX o0Y c~


Foreshortened Sketch
RELATION OF LITHOLOGY TO OFFSHORE PROFILES
ALONG THE WEST COAST, FLORIDA PENINSULA


Figure 16. Foreshortened sketch showing the relation oflithology to offshore profiles along the west coast
of the Florida peninsula



































S 2 3 4 5 MILES fti :



Figure 17. Air photo showing characteristic pattern of Ten Thousand Islands





GEOLOGICAL BULLETIN NO. 51


profile been cut out by wave erosion. Similarly the partly drowned
crescentic dunes that form Cedar Keys and Horseshoe Beach in
Suwannee Bight at the north would also have been destroyed in
shoreline retreat had this broad bight been cut out by wave erosion.
Where quartz sand has been continuously available in preextant
rocks such as the Miocene sediments of the mid-peninsular west coast,
seaward migration of shorelines seems to have been going on for a long
time through successive transgressions. This seems to explain the broad
succession of relict beach ridges and barriers that characterize the
protuberant part of the peninsular Gulf coast between Anclote Key
and Cape Romano. Apparently transgressions cresting at lower sea
levels than previous ones or at approximately comensurate ones have
added new seaward increments to a coast that has been repetitively
progradational.
The Ten Thousand Islands are an interesting transitional section
of coast, figure 17. They are founded on the Tamiami Limestone which
supplies little sand, but a drift of sand across Gullivan Bay from Cape
Romano Shoals supplies enough sand to allow an impersistent barrier
to accumulate as the outer islands of the Ten Thousand Islands. But
this barrier is not accompanied by the characteristic wave-scoured
off-shore profile that brings the five fathom isobath within a mile of the
beach.
By contrast with these protuberant sand-dominated coasts, areas
floored by rocks that do not readily supply sand to the shore-forming
processes tend to maintain shorelines which are less affected by ero-
sional and depositional littoral processes. Such shorelines tend to be
located where sea level intersects the previous subaerial slope rather
than where waves tear up the bottom and throw up barriers as they do
on sandy bottoms. Such shorelines therefore tend to be reentrant
rather than protuberant, as south of Cape Romano, and north of
Anclote Key in Suwannee Bight.
Since they build few barriers or beach ridges these reentrant
shorelines are much more migrant shifting their geographic location
markedly with each nuance of sea level change because their profiles
are so exceedingly gentle (about one foot per mile seaward slope). Such
conditions gradually dissipate wave energy before it reaches the shore.
And since every minor change of sea level causes the shoreline to
migrate some considerable distance this continually changes the place
at which shore processes operate and further thwarts their efforts to
cut an erosional shore. However, despite this migration of shore line
during a rapid transgression, the coast seems to have gone through a
progressive evolution of type in the 4000 years of essentially stable sea
level since cresting of the Flandrian transgression.





BUREAU OF GEOLOGY


Sandy shores may remain fairly securely localized where a barrier
or beach ridge has beenbuilt. Because of their steep profile they are not
as subject to great migration with minor sea level change if sand supply
is adequate to maintain equilibrium.
Since the sand-deficient parts of the Florida peninsular West
Coast result from submergence of an extremely gently sloping, and
very flat limestone terrain, the resulting shorelines are characteris-
tically marshy, incorporating a wide zone of gradually deepening water
in a broadly gradational shore zone that changes slowly over several
miles. It begins offshore with open shallow marine water that grades
through various kinds of mangrove or other salt marsh, to fresh water
swamp, usually with a plexus of more or less open water ways.
The details of this gradation change with the nature of the terrain
that has been transgressed. Each of the several geologic formations that
outcrop along the southwestern coast of the peninsula can be delin-
eated in the shore zone by the changes its distinctive rock imposes on
this general pattern of coastal features. Thus, the nature of the shore-
line is to a large extent a matter of indirect lithologic control. The
tamiami formation is associated with the Ten Thousand Islands. The
Anastasia formation is coextensive with an area of straighter, more
integrate coastline adjacent to the Ten Thousand Islands on the south
which is influenced by the debouchure of the Everglades Sloughs. And
the coastal prominence that is Cape Sable overlies Miami Oolite.
Although these relations between geologic formations and coastal
types are rather well defined, the reasons for the characteristic peculiar-
ities of each of the three coastal segments are difficult to establish.
Thus the salient of Cape Sable, although it correlates with and overlies
the distal end of the coastal zone where the Miami oolite outcrops, is
largely built of post-Flandrian coquinoid beach ridges that are sepa-
rated from the nearest surface exposures of oolite by broad areas of
peat and marl and the lagoon-like Whitewater Bay. The oolite here is a
degenerate southwestern extension of the Miami Ridge, which forms
the low partial divide between the Everglades Sloughs and Florida Bay.
Either it was a very weak feature here to begin with or has been greatly
reduced in stature by solution, as buried stream channels in its upper
surface suggest (Spackman, Scholl and Taft, 1964). Nonetheless, it
seems to have formed a low ridge that localized the coastal salient of
Cape Sable. Spackman, Scholl and Taft (1964, figure 58) in a block
diagram of this region show the surface of the Miami oolite high under
Cape Sable and falling away to lower elevations to north and south.
They also present a cross section (their figure 34) which shows a
shallow submarine scarp cut into the oolite beneath Cape Sable. Again




GEOLOGICAL BULLETIN NO. 51


their figure 27, "Structural Contours on Miami Oolite", in the vicinity
of Whitewater Bay, landward of Cape Sable shows the top of the oolite
higher behind the cape and falling to lower elevations both southeast-
ward toward the mouth of Florida Bay and northward toward the edge
of the Everglades Sloughs as typified by the Shark River.
Perhaps this shallow, wave-cut notch in the oolite bedrock local-
ized wave-breaking long enough to allow a bar to build up and form a
barrier. Apparently the resulting environment of open, clear, sea water
and higher wave energy fostered growth of shell fish. Their shells seem
to have enabled the barrier to maintain itself, anchored on the notch in
the oolite, building up in the same place as sea level rose to its present
elevation. Minor changes of shoreline here of both progradation and
regression are shown by the pattern of relict beach ridges and micro-
lagoons which dominate a narrow zone immediately landward of the
present beach (Spackman, Scholl and Taft, 1964: Craighead, 1964).
Adjacent to this area of high, oolite bedrock on the north was the
low broad, bedrock swale of the Everglades Sloughs founded on the
Anastasia formation. There the waves of the Gulf of Mexico went
farther eastward before they felt the bottom enough to break. This
seems to have allowed the Cape Sable area to become a broad coastal
prominence built on the western end of the Miami Ridge between two
reentrant sections of coast, Florida Bay to the south and the area of
debouchure of the Everglades Sloughs to the north. This peninsular
situation seems to have produced a coast-parallel drainage exemplified
by the Joe River which flows northwestward along the southwestern
edge of Whitewater Bay. Probably storm levees (Craighead, 1964) built
along the north shore of Florida Bay during hurricanes prevented Joe
River and Whitewater Bay from draining southeastward to Florida Bay.
However, there are features in Whitewater Bay which suggest that
it occupies an area that formerly drained southwestward toward the
present cape through many sub-parallel, coast-perpendicular avenues
oriented like the Everglades Sloughs adjacent to the northwest. Such an
early post-Flandrian drainage pattern may have been inherited from a
similarly oriented pre-Flandrian one, relicts of which (Spackman,
Scholl and Taft, 1964, figure 27) are preserved in the oolite bed rock
beneath the post-Flandrian marls and peats of the present surface.
When water tables rose, as the Flandrian transgression neared its crest,
these coast-perpendicular drainage ways began to accumulate peat. But
they still maintained the coast-perpendicular orientation that is charac-
teristic of mainland drainage ways near the coast all around the low
distal part of the Florida peninsula. However, as the bedrock-anchored
barrier began to develop at Cape Sable and the resulting lagoon began





BUREAU OF GEOLOGY


to accumulate sediment (mostly peat according to Spackman, Scholl
and Taft, 1964) these coast-perpendicular drainage ways not only
became over extended in an untenable direction of flow parallel with
the axis of a promontory, but they had a barrier athwart their mouths
in the person of the beach ridges of Cape Sable. Possibly for this reason
either Joe River or a drainageway in the area now occupied by White-
water Bay initiated a right-angled change of drainage direction letting it
escape laterally from the north side of the Cape Sable promontory to
the adjacent low area occupied by the Shark River at the Southeastern
edge of the Everglades Sloughs.
The relicts of the original coast-perpendicular drainage seem to be
manifest in the nearly parallel orientation of long attenuate islands in
Whitewater Bay which are elongate in the northeast-southwest direc-
tion that is characteristic of all coast-perpendicular drainages of the
southwestern coast of the Florida Peninsula between Cape Romano
and the Shark River.
Spackman, Scholl and Taft (1964) discussed wave or current
erosion of the peaty islands of Whitewater Bay and they also have
discussed development of marl levees along waterways in this area.
Possibly the erosion they described has produced the present open
water of Whitewater Bay through wave erosion induced by cresting of
the Flandrian transgression after the bulk of the peat had been de-
posited. The marl levees may, in large measure, be responsible for the
long narrow islands and peninsulas of the southwest side of Whitewater
Bay that seem to be relicts of the earlier southwesterly drainage built
up on the peat that is now rapidly being destroyed by erosion.

Beyond Whitewater Bay to the southwest between the Joe River
and Cape Sable proper, the drainage seems to have become an isolated
poccosin for that area is now mostly a peat dome sloping downward in
both directions; both northeastward to the Joe River and Southwest-
ward to the micro Lagoons landward of Cape Sable (Spackman, Scholl
and Taft, 1964, figure 34).
By contrast with the Cape Sable coastal prominence the area of
outcrop of the Anastasia formation adjacent to the oolite on the north,
localizes the Everglades Sloughs, the broad zone of braided drainage-
ways that drain the Everglades to the Gulf of Mexico. Possibly this
drainage is located here because it was deflected westward by the oolite
ridge rather than because of any peculiarity of the Anastasia formation
over which it flows. But, whatever the reason for the Everglades
Sloughs being in the zone of outcrop of the Anastasia formation their
large discharge of fresh water has probably helped to lower the profile




GEOLOGICAL BULLETIN NO. 51


of this area by solution of the underlying shelly limestone thus ac-
counting for the reentrant character of its coastline.
The features sometimes called Back Bays are lagoon-like bodies of
open water that extend more or less continuously from Naples at the
north to Whitewater Bay at the south. It seems instructive that they all
but disappear in the peat-surfaced area where the voluminous fresh
water discharge of the Everglades emerges in the southern part of the
area of exposure of the Anastasia formation. There many of the
coast-perpendicular drainage ways still preserve their identity across
the zone which elsewhere seems to have been dissected by wave and
current action to form the open water of the Back Bays. On the flanks
of the Everglades Sloughs section of the coast these coast-perpendic-
ular stream channels gradually lose their identity in crossing the Back
Bay zone. Thus, Lostmans River to the north has two discrete branches
that fork on the seaward or barrier side of the Back Bays, continue
eastward across the zone of the Back Bays as widened, lake-like water
bodies separated by narrow septa of insular and peninsular land, and
persist discretely northeastward into separate headwater areas on the
mainland.
Whatever the reason for the lagoon-like Back Bays, it seems fairly
clear that the voluminous flow of fresh water from the Everglades has
favored the growth of peat to the extent that they have not been able to
form (or perhaps have not been able to maintain themselves as bodies
of open water) in the area of debouchure of the Everglades Sloughs.
Only in this section of the coast does peat extend all the way to the
shore of the open Gulf of Mexico giving it a smoother, less ragged
shoreline. Elsewhere, to the north and south, a zone of marine marl or
shell intervenes between the edge of the peat and the shore of the Gulf
of Mexico.
These observations suggest that the area across which Everglades
water debouches has progressively narrowed from a wider zone which
originally extended both northwestward beyond Lostmans River and
southeastward across much of the area now occupied by Whitewater
Bay.
Deprived of the voluminous fresh water discharge necessary to
maintain peat growth by excluding the salt water, these flank areas
seem to have become subject to erosion, producing Whitewater Bay to
the southeast and the more southerly of the Back Bays to the north-
west. Their lagoon-like form may result from the former juxtaposition
of peat to landward and marine marl to seaward. The more resistant
marl remained as a pseudo-barrier while the more vulnerable peat was
eroded out to form a pseudo-lagoon (Back Bay). Similar juxtaposition




BUREAU OF GEOLOGY


of resistant marl and vulnerable peat may account for the remnant marl
levees (Spackman, Scholl and Taft, 1964) that delineate the relicts of
the former drainage avenues in Whitewater Bay and where Lostmans
River formerly crossed the area of the present Back Bays.
There has been much concern about the conservation problems
associated with lowered water tables in the Everglades, and it may be
that this apparent narrowing of the area of debouchure of the Ever-
glades in another result of reduced fresh water discharge. Erosion of the
shorelines of islands and peninsulas in Whitewater Bay is great enough
to show conspicuously on aerial photographs taken at different dates
(Spackman, Scholl and Taft, 1964). In a broader sense, this may mean
that the present artificially-made drought is undoing the work that a
rising water surface began at the crest of the Flandrian transgression.
However, the plan of the Back Bays on the map seems too
systematic to be wholly a product of differential erosion as Spackman,
Scholl and Taft (1964) thought. It follows the great geometric curve of
the coastline between Capes Romano and Sable with more faithfulness
than the present oceanic shore does. Moreover, it follows two concen-
tric, similar curves which overlap for a short distance in the northern
part of the Ten Thousand Islands (P1. 1). This suggests that they are
differentially derelict remnants of degenerate lagoons. These lagoons
were probably enclosed behind barriers of sand at the north in the Ten
Thousand Island area (see below), and behind shell bars farther south.
With passage of post-Flandrian time the preservation of low-energy,
swampy conditions allowed mangrove and fresh water swamp deposits
to mask their original character and render them derelict.
It seems instructive that these old lagoons are most degenerate
where the regional slope to landward is gentlest. Thus, as the Back
Bays, they persist southeastward as far as the steeper slope of the Big
Cypress (the area of exposure of the Tamiami sandy limestone) does.
But farther south in the virtually horizontal area of the Everglades
Sloughs they are wholly occluded by peat because it is through this low
flat trough that the Everglades debouched most of their great discharge
of fresh water. This broad sweep of fresh water was the maintaining
force of the peat and, now that it has been reduced by diverting
drainage works, the occluded lagoon seems to be reappearing as the
occluding peat is eroded out of it. The attenuate inlands and peninsulas
of Lostmans River and Whitewater Bay, and the isolated marl levees are
resistant remnants of a once more continuous mass that show the
progress of this exhumation of the occluded lagoon. However, one can
not think of Whitewater Bay as a feature dominantly made by modern
artificially induced erosion. Apparently there have been natural




GEOLOGICAL BULLETIN NO. 51


changes of circumstance that have sometimes helped agradation and
sometimes erosion. Thus, the rock floor of the Everglades Sloughs has
an axial valley that seems to have been made during a period of
reduction but it was covered by a broad blanket of peat made during
times of agradation.



THE TEN THOUSAND ISLANDS

The coastal area adjacent to the Big Cypress is known as the Ten
Thousand Islands. It differs from adjacent sections of the coast to the
north and south and seems to be a gradation between them. The Ten
Thousand Islands begin at the north in the Lee of Cape Romano at the
southern end of the sand-dominated section of the coast. Unlike the
coast farther south, quartz-rich sand forms short beaches around the
outer shores of the outer islands but it is not available in sufficient
quantity to allow these beaches to coalesce and form a continuous
barrier like those which prevail along the sand dominated coast to the
north of Cape Romano.
Landward of these beach rimmed outer islands are the rest of the
many islands that give this intricate archipelago its name. Most of these
inner islands are made of oyster shell (Crassostrea virginica) and are
surmounted by mangrove. Between the Ten Thousand Islands and the
mainland lies the generally open water of the Back Bays (Chokoloskee
Bay, etc.).
Shier (1969) found that the outer, beach-rimmed islands were
generally defended by cores of vermetid reef rock (Vermetus (Thylaeo-
dus) nigricans). He agreed with Scholl (1964) that the sand of the
beaches was transported across greater Gullivan Bay from the Cape
Romano shoals. In the lee of these vermetid-reef-founded outer islands
he thought the inner oyster-founded islands grew up in the lagoonal
waters during late-Flandrian time.

THE SILVER BLUFF RIDGE AND SCARP

The Miami Ridge and associated Silver Bluff Ridge were probably
more or less coeval with the Key Largo Reef. Their maximal elevations
seem to be about the same, all being about the right height to correlate
with Pamlico sea level. The Miami Ridge seems to have been a Pamlico
oolite shoal which reached its best development where arterial tidal
overwash could pass around the northern end of the Key Largo Reef.




BUREAU OF GEOLOGY


Both the Miami Ridge and the Silver Bluff Ridge lose stature and
definition as they extend southwestward behind the Key Largo Reef.
The southwestern part of the Miami Ridge may have lost stature from
solution by freshwater overflow southward from the Everglades, but it
seems to have been best developed as an oolite shoal at the northeast
where it was open to surf and tide.
More definite information on the simultaneous growth of the
Miami and Silver Bluff Ridges can be had from the plan of the Silver
Bluff Ridge which parallels the Miami Ridge on the east and seems to
have been its seaward barrier in Pamlico time. Since the Silver Bluff
Ridge has the form of a coastal arc or beach crescent (P1. 2) and is only a
few hundred feet wide it is obvious that it has not been greatly
modified by post-Flandrian coastal erosion otherwise it would have
been transected and dismembered by the erosion. Its relation to the
relict mangrove islands of the Miami Ridge shows it to have been extant
while they were being built. It turns up the valley of the Miami River in
the manner of an inlet ridge (the curved extension of a beach ridge
turned landward along the shore of a tidal inlet in a barrier island). And
as can be seen on plate 2 this landward-turning extension of the Silver
Bluff Ridge merges with and becomes part of the first ring-shaped relict
mangrove island south of the Miami River. This establishes the simul-
taneous origin of the Silver Bluff Ridge and the relict mangrove islands
of the Miami Ridge behind it, since they were both built up to the same
pre-Wisconsin sea level. And it places this former sea level near the top
of the Silver Bluff Ridge during the time the ridge was being built
because it is essentially the same height as the adjacent relict mangrove
islands to the west which by analogy with modern mangrove islands
should have had elevations very close to their contemporary sea level.
The internal construction of the Silver Bluff Ridge also offers
evidence that it was largely awash when it was built because it is almost
wholly made of cross-bedded oolite sand with most of the crossed beds
dipping seaward (east). Only on the gentler, western slope of the Ridge
do they occasionally dip landward (west).
The "Silver Bluff shoreline" is a wave-cut berm and scarp on the
east side of the Silver Bluff Ridge. The scarp seems to have originated as
the seaward edge of the Silver Bluff Ridge when it was built as an oolite
shoal in Pamlico time with its crest essentially at the level of the
Pamlico stand of sea. But it seems to have been modified by the attack
of waves during three different times of sea levels lower than that of the
Pamlico stand. One at about 10 feet above present sealevel, one at
about half that and lastly, it seems to be under occasional attack by
certain hurricane-gotten waves of the present water of Biscayne Bay. It





GEOLOGICAL BULLETIN NO. 51


is probably the most obvious scarp of the Coastal Plain. Named for the
community of Silver Bluff in Miami (which in turn seems to have been
named for the scarp), it is seen dramatically along the northwest side of
South Bay Shore Drive. It crosses South Bay Shore Drive near the west
corner of the grounds of Mercy Hospital and a few hundred yards to the
northeast it was used to dramatize the entrance to the grounds of
Vizcaya, the house of the late John Deering, where a broad stairway
descends the scarp just beyond the present ticket-seller's booth which
is situated at its crest.

In several places along South Bay Shore Drive the Silver Bluff
Scarp shows the character that seems to have gotten it its name. Here it
is an obvious wave-cut cliff of varying stature up to some 15 feet from
crest to toe. In a few places the crest of the Silver Bluff Ridge reaches
elevations above 20 feet, among the highest natural elevations in south
Florida; at least roughly commensurate with the highest parts of
presently unmapped Key Largo. The scarp is cut into the Miami oolite
of the Silver Bluff Ridge and stands sharp and vertical as a wall of
surficially indurated rock showing neither slump nor soil development
(Fig. 18). In the coastal plain such an abrupt topographic feature could
not fail to become a subject of geologic curiosity, and several geologists
have noted its peculiarities, notably Parker and Cooke, (1944), Cooke
(1945), Parker and others (1955).

Parker and Cooke, (1944, p. 24) referred to 5 and 8 foot benches
and suggested that they were cut by wave erosion during regression of
the Pamlico sea. Cooke (1945) regarded the Silver Bluff Scarp as dual,
cut by sea levels ten and five feet above present sea level. Evidence for
wave erosion at the ten foot level is sparse and if there was a prominent
scarp with a toe at ten feet, it has apparently been largely destroyed in
the cutting of the younger and lower one. Although in the center of the
broad topographic swell between Franjo at the Southwest and Cutler at
the northeast (Perrine 7V2" sheet) elongate, closed, fifteen-foot con-
tours suggest a relict, low, emergent bar like the present Bahaman cays
south of Bimini along the western edge of Andros Bank. This may well
have been associated with the upper of the two relict benches noted by
Parker and Cooke.

Most of the evidence for an eight or ten foot toe was obtained
from the vicinity of the Miami River where the upper part of the Silver
Bluff Scarp turns inland up the south valley wall of the river and the
lower part ends at Point View, a prominence in the mainland shore at
the edge of the flood plain about three quarters of a mile south of the
river mouth.








































Figure 18. The Silver Bluff Scarp on South Bay Shore Drive where it seems to have been freshened by
recent wave erosion during certain hurricanes





GEOLOGICAL BULLETIN NO. 51


Adjacent to the Miami River this floodplain or transverse glade is
about a mile wide through the lower two or three miles of the river's
valley. Like most of the other transverse glades it widens up-stream
toward the Everglades while the adjacent interfluves gradually lose
elevation in the same direction until both uplands and lowlands lose
topographic distinction and merge to a common low plain where the
west flank of the Miami Ridge slopes down to become the Everglades.
Most plausibly this stream-side flat is a relict pre-Wisconsin tidal
channel. It has two prominent slough-like channels which seem to be
relict tidal creeks developed on it as it emerged to become a tide flat. As
well as can be determined from the five-foot contour interval of the
topographic maps, elevations on the relict tide flat are between five and
ten feet. Those of the relict sloughs are between zero and five feet.
Plausibly these two surfaces correlate with those of comparable eleva-
tion in the Coral and Oolite Keys. At its edges this relict tide flat rises
abruptly to the ring-shaped ridges or relict mangrove islands which
frequently attain elevations roughly commensurate with those found
at the crest of the Silver Bluff Ridge. I believe this abrupt rise is the
scarp with the eight to ten foot toe mentioned by Parker and Cooke.
But here along the edge of the transverse glade traversed by the Miami
River it is the outer edge of a relict mangrove island of Pamlico time and
the elevation of its toe may have been determined by the depth of scour
of the tidal currents that flowed through this transverse glade when it
was a Pamlico tidal sluiceway rather than by a sea level lower than
Pamlico. The 8 or 10 foot scarp toe of the Silver Bluff iay correlate
with the surface of commensurate elevation in the Coral Keys and
similarly the five foot toe may be a correlative of the surface of the low
Coral Keys and the Oolite Keys. Such a correlation would lend cre-
dence to the idea that the Silver Bluff Scarp had been attacked by
waves during levels of sea some 5 and 10 feet higher than present sea
level. But the alternative idea that the 8 to 10 feet level is a relict of the
base of tidal scour in Pamlico time casts some doubt on the idea that
the Silver Bluff Scarp was significantly affected by wave erosion during
a ten foot sea level. Apparently wave energy was usually rather low here
because of the offshore barrier provided by the Coral Keys.

The spectacular sharpness of the Silver Bluff Scarp fades away to
the southwestward along the mainland shore of Biscayne Bay. It can be
seen very easily along Old Cutler Road east of Perrine but it is a gentle
slope rather than a cliff. Little rock is seen and all parts of the profile
are soil covered. Still farther to the southwest the scarp becomes so
gentle in slope it is hardly discernable on the ground, but can be found
on the topographic map of one-foot contour interval made by the Soil




BUREAU OF GEOLOGY


Conservation Service of the United States Department of Agriculture.
Apparently the Scarp is sharper and more precipitate at the northeast
because it is still exposed to occasional vigorous wave erosion during
hurricanes. Farther southwest where it lies in the lee of the Coral Keys
it seems completely derelict.
I think this sharper part of the Silver Bluff Scarp is jointly a
post-Flandrian product of recent wave erosion at present sea level and
of pre-Flandrian wave erosion during the stand of sea level that bevelled
the surface of the Low Coral Keys and the Oolite Keys and I believe it is
still occasionally an active shoreline. Its superficial appearance as a cliff
cut into obdurate consolidated rock is misleading. Most geologists who
have worked with the Miami oolite are familiar with its ability to
develop an indurated surface where it is subaerially exposed. This
ability is seen in Figure 19 which shows two adjacent excavations in the
Miami oolite at the crest of the Silver Bluff Scarp near Brickell Avenue
in Miami. In the foreground is a vertical surface cut into the oolite to
grade the street some years ago. In the background is a new excavation
which was being made at the time the photograph was taken. The wall
of the older surface in the foreground is now indurated rock, yet earth
moving equipment designed for incoherent materials (ditching ma-
chines and bulldozers) had no difficulty removing oolite within a few
inches of this hardened surface.

Again at the crest of the Silver Bluff Scarp at the intersection of
southwest 22nd Avenue and Kirk Street in Silver Bluff I had little
difficulty putting a hole down five feet with an ordinary soil auger after
spudding through a few inches of hardened crust.

Obviously the Silver Bluff Scarp gives a false impression of dura-
bility. It is not a cliff cut into consistently hard rock but a case-
hardened bluff cut into incoherent oolite. But if it is subject to only
rare attack and only by the big waves of hurricanes its freshly wave-
bitten face may have time to develop a hardened protective crust
during the intervals between such rare attack by waves.

I think the Silver Bluff Scarp has been cut back in very recent
times during certain hurricanes when high on-shore winds and low
barometric pressures were forcing water into Biscayne Bay and causing
abnormally high tides. Under these circumstances the surf would wash
away the debris from the toe of the scarp, undermine the case-hardened
part, and erode it back farther. There is little case hardening on the
bench at the toe of the scarp because vegetal cover and wet marly fill
usually prevent it.




GEOLOGICAL BULLETIN NO. 51


Figure 19. West side of Brickell Ave., Miami, showing indurated wall
of old excavation in foreground and new cut in incoherent
oolite behind it

In the summer of 1965 there was extensive ditching along South
Bay Shore Drive in Silver Bluff in the area along the toe of the scarp
where it is most sharply cut. Excavations to depths of four and five feet
showed no identifiable Miami oolite in place. Instead there was a
variety of stratified fill including an organic-rich layer at a depth of
about three to four feet. Probably this last was a natural subaerial
surface. Its overburden may have been largely artificial. However, the
organic layer was barely above present sea level at horizontal distances
less than 75 feet from the toe of the Silver Bluff Scarp. This argues
against the idea that the present face of the scarp here was cut by a sea
level appreciably higher than the present one.




BUREAU OF GEOLOGY


9- 'ii




















Figure 20. Silver Bluff Scarp in distance seen from the shore of
Biscayne Bay


The relation between the natural ground surface at the toe of the
Silver Bluff Scarp and present sea level can be seen at several other
places along the mainland shore of Biscayne Bay. Where the natural
ground surface is seen in section it is not more than a foot to eighteen
inches above sea level. Figure 20 shows a photograph taken from the
shore of Biscayne Bay a few hundred yards south of "Spoil Bank" at
the mouth of Cutler Canal. The toe of the Silver Bluff Scarp is seen in
the distance where the road slants up the hill near the Palm tree. The
water in the ditch alongside the road is sea water. It is no farther below
the surface of the ground at the toe of the scarp than it is in the
oreground of the photograph.




GEOLOGICAL BULLETIN NO. 51


Figure 21. Shore of boat basin off Coral Gables Canal


Again near the Coral Gables Water Way (Fig. 21) the natural
ground surface, marked in figure 21 by the top of the darker, finer-
textured zone at the bottom of the bank is barely above sea level at a
distance of some few tens of feet from the toe of the Silver Bluff Scarp.
At the mouth of Cutler canal near "Spoil Bank" the photograph (Fig.
25) shows artificial fill at the toe of the Silver Bluff Scarp. Fifty to one
hundred feet to left or right of the canal the natural mangrove swamp
lies directly along the toe of the scarp at elevations less than a foot.
Even the most active sea cliffs do not have their toes at sea level.
The wave-cut bench characteristically slopes up to the toe of the cliff at
elevations several feet above sea level. This elevation is determined not




BUREAU OF GEOLOGY


by sea level alone but by height of tides, size of maximal storm waves,
quantity and texture of debris, off-shore slope, etc. With maturation of
erosion and establishment of a profile of equilibrium where a cliff is cut
out of unconsolidated sediment the ephemeral influence of excep-
tional high tides and big waves is more effective because equilibrium
profiles are temporarily violated by higher water levels and significant
erosion can be effected in a very short time. Thus, the Silver Bluff
Scarp, cut out of incoherent oolite, should be a good place for such
high tides and big waves of hurricanes to effect significant erosion
despite their short duration.
The direction of maximum-speed winds in the Miami area is
generally from the east; the direction necessary to bring hurricane
waves through the mouth of Biscayne Bay and allow them to break
along the mainland shore where the Silver Bluff Scarp has its most
freshly cut appearance. Before the southward growth of the barrier to
form Virginia and Biscayne Keys these high waves would have had
more direct access to the scarp.
A few hundred yards southwest of the mouth of Cutler Canal
there is good evidence that hurricane seas can reach the Silver Bluff
Scarp. Figure 22 shows a twenty-five foot sailboat that Hurricane
Donna (1960) washed across some 1,000 feet of what is ordinarily dry
land, and dropped within fifty feet of the toe of the Silver Bluff Scarp.

The internal structure of the Silver Bluff Ridge supports the idea
that it has largely been formed as a shallowly submerged bar. (Hoff-
meister, Stockman and Multer, 1967, p. 185.) Most beach ridges are
dominantly made of sand that has been blown landward from a dry
beach berm and filtered down into dense, scrubby, spray-stunted
vegetation. Although essentially aeolian, such accumulations of sand
show little of the crossbedding characteristic of non-vegetated, march-
ing dunes. The Silver Bluff Ridge by contrast is built dominantly of
cross-bedded oolitic sand that seems to have been emplaced by water
rather than wind and the seaward dip of most of the cross-bedding
suggests that the Silver Bluff Ridge was built at a higher sea level when
most, if not all, of its present subaerial stature was submerged.
The present mainland lagoonal shore between Pompano Beach
and Miami seems to be a relict pre-Wisconsin oceanic shore reactivated
at present sea level or at least a recent shore line that closely resembles
the last pre-Wisconsin shore line that is still above sea level. Both this
present shore line and its relict predecessors have been cast into a series
of concentric arcs that are somewhat similar to those between the
Carolina Capes farther north (Cape Hatteras, Cape Lookout and Cape




GEOLOGICAL BULLETIN NO. 51


Figure 22. Twenty five foot sailboat washed across some 1000 feet of
what is ordinarily dry land by hurricane Donna in 1960

Fear in North Carolina) which also seem to have been shaped under the
influence of geometrically similar relicts of earlier shore lines to land-
ward (White, 1966).
The mainland lagoonal shores of the coast of southeastern Florida
have been cut off from the waves of the open ocean by a sand barrier as
have those of the lagoons between the Carolina Capes, but there is a
major difference in the way this occultation was done.
In the Carolinas, from Core Sound southward, the lagoonal main-
land shore and the oceanic shore of the barrier are geometrically similar
and essentially concentric. The present oceanic shore line of the barrier
mimics the older oceanic shore line that forms the present mainland




BUREAU OF GEOLOGY


shore of the lagoon. All parts of the barrier seem to be essentially coeval
along its length and the lagoon has a rather uniform width along its
length. This tendency for the barrier to mimic the mainland shore is
generally characteristic of the coast north of the coastal salient at Palm
Beach because shallow shelf waters intervene between the barrier and
the edge of the continental slope.
In Southeastern Florida on the other hand the barrier does not
simulate the relict coastal arcs of the mainland lagoonal coast. Instead
it extends nearly straight southward from Pompano Beach to Cape
Florida. Apparently it has been localized by some influence that is
quite independent of earlier oceanic shores; possibly the outer edge of
shoal water along the crest of the continental slope.
The barrier differs from its Carolinian counterpart in its manner
of growth as well as in its shape. All parts of the Carolinian barrier are
essentially coeval, but the barrier of southeast Florida seems to have
grown southward like a spit; its northern part being the oldest and its
southern distal end the youngest so that it cut off the mainland shore
from the oceanic surf increasingly later with distance southward.
Thus dereliction of these mainland coastal arcs of southeastern
Florida is increasingly older to the north. The original post-Flandrian
headland seems to have been near Lettuce Lake near the southeastern
corner of the city of Pompano Beach (P1. 3). The northernmost relict
shoreline arc begins there and extends southward along the mainland
side of a derelict lagoon curving, at first, abruptly westward and then
southward with more gentle curvature to the latitude of the north end
of Hugh Taylor Birch State Park in Fort Lauderdale.
Before this shoreline arc had been long exposed to the attack of
the surf from the open ocean a spit-like barrier grew southward across it
from the original headland at Pompano Beach. This barrier cut off the
mainland shore of the lagoon from the open ocean and it became
derelict as far south as the barrier-spit reached. Farther south, however,
the mainland shore was still open to oceanic surf which continued to
maintain a second shoreline arc very similar to the first between the
southern end of the first one and the west end of North Lake in eastern
Hollywood. Like the first shoreline arc this second one was later cut off
from the open ocean by southward growth of the barrier and it in turn
became derelict.
This process of occultation of successive arcs along the mainland
shore seems to have continued until five such arcs were produced (P1.
3). The third extended from Hollywood to North Miami Beach, the
fourth, from North Miami Beach to Point View, and the fifth or present





GEOLOGICAL BULLETIN NO. 51


one, from Point View to the southern part of Biscayne Bay where the
mainland shore has long been protected against erosion by the interven-
tion of the Coral Keys between it and the ocean.
The sequence of events suggested here is supported by differential
dereliction of the five parts of the lagoon involved. The part of the
lagoon that lay before the first or most northerly of these shoreline arcs
is so degenerate that it shows no open water at all and little marsh or
swamp. That which lay before the second shoreline arc still shows
occasional bodies of open water although most of its eastern part is
mangrove, and there is a considerable zone of low dry land adjacent to
the original oceanic coastal scarp. Areas of both mangrove and open
water increase in the third section of lagoon. The fourth section is the
open water of the narrower northern part of Biscayne Bay north of
Point View and the mouth of the Miami River. The fifth is the main
body of open water of Biscayne Bay itself.
Before the barrier began to grow southward from the first head-
land at the north near Pompano Beach, the entire reach of mainland
shore was subject to oceanic surf. But when the barrier cut the waves
off from the northernmost shoreline arc, this arc became derelict while
the remainder of the mainland shore to the south was still an active
shoreline of the open ocean. As the barrier grew southward by another
increment the second shoreline arc was cut off from the oceanic surf,
and it too began to degenerate. Similarly the third and fourth shoreline
arcs have been successively cut off from the ocean as the barrier added
the increments needed to occult them.
The fifth shoreline arc, the Silver Bluff Scarp, adjacent to the
main body of Biscayne Bay south of Point View, has not yet been
wholly cut off from the ocean since the barrier chain ends at Cape
Florida; and the occultation process is not complete.

In the case of the last two shoreline arcs, the fourth and fifth, each
one shows that it is younger than the next one to the north by crossing
the lagoon. Thus, as the fourth shoreline arc curves more sharply
eastward toward its northern end, it truncates the sediments (mangrove
swamp) of the more degenerate section of lagoon associated with the
adjacent third shoreline arc to the north.
The fifth mainland coastal arc is the Silver Bluff Scarp, and like
the other four mainland coastal arcs to the north, the Silver Bluff Scarp
curves increasingly eastward as it approaches its northern end near the
mouth of the Miami River at Point View. If this curve were extended
out into Biscayne Bay it would separate the wide, southern part of the
bay from the narrow northern part and would intersect the present




BUREAU OF GEOLOGY


barrier at the southern tip of the island that is occupied by the main
part of the city of Miami Beach. The barrier south of that point (mostly
Virginia Key and Biscayne Key) seems to be late additions to the
barrier chain still following the repetitive pattern of cutting off the
mainland coastal arcs from oceanic surf and rendering them derelict.
The apparent late dereliction of the Silver Bluff Scarp is probably a
product of this latest southward extension of the distal end of the sand
barrier. Perhaps with time the barrier will grow southward far enough
to close the mouth of Biscayne Bay and completely occult the Silver
Bluff Scarp. But the general dearth of sand in the peninsula below this
attitude suggests that the barrier has already grown about as far
southward as its sand supply will permit. Also the seaward turn of the
distal, southern end of Biscayne Key at Cape Florida suggests a sea-
ward-setting current there which shunts the southward drifting sand
into the deep water of the Florida straits. If this be true it would seem
improbable that the barrier should ever grow much farther southward.
The controlling factor is the major coastal prominence at Palm
Beach. Northward from Palm Beach the coastline lies increasingly
farther back from the edge of the continental slope. At Palm Beach the
edge of the continental slope intersects the land and southward from
that point the shoreline can not prograde appreciably because of deep
water closely off shore. The five coastal arcs in question occupy most
of the Atlantic coastline south of Palm Beach which forms a great
coastal prominence similar to that of the North Carolina Coast which
seems to have caused the development of the three similar coastal arcs
to the south of Cape Hatterras between Cape Hatteras, Cape Lookout,
Cape Fear and Cape Romain (White, 1966). In both instances, Florida
and the Carolinas, there are southward-setting longshore currents along
the segments of coast in question at least in part. In the Carolinas the
present barrier is able to mimic the older mainland shore because there
is shallow shelf water offshore to allow the off-cape shoals to extend
the headlands (capes) seaward and maintain the coastal arcs between
the capes. In southeastern Florida on the other hand the present barrier
has been built southward essentially at the edge of the deepening water
of the continental slope and therefore the headlands between coastal
arcs could not maintain off-cape shoals to separate coastal arcs.
In the Carolinas (south of Cedar Island) the coastal arcs are
expressed in both the mainland shore and in the barrier as well. But in
south Florida they are not expressed in the plan of the barrier but
rather in the mainland shore and the contemporaneous southern ends
of lagoons as the barrier grew distally southward. This is because in the
Carolina Cape zone sand supply is voluminous, the shelf is wide and




GEOLOGICAL BULLETIN NO. 51


slopes gently seaward. Therefore prominent off-cape shoals could
maintain themselves and partition the coast into coastal arcs even
during rising sea levels following glacial regression (White, 1966).
But in the southeastern coast of Florida sand supply for longshore
drift is increasingly small with distance southward and sand is probably
lost to transport down the continental slope to the deep Florida straits.
For all these reasons off-cape shoals could not maintain themselves far
enough eastward to influence the plan of the present barrier which is at
the crest of the continental slope at the edge of deep water.
Thus, in the Carolinas, all parts of the mainland lagoonal shore-
lines were made at the same time. Although the oceanic barrier shores
may be younger, they also seem to have been built simultaneously
throughout, and both mainland and barrier have similar, concentric,
coastal arcs. In southeastern Florida the barrier is increasingly younger
with distance southward toward its distal end. The coastal arcs of the
mainland lagoonal shores of southeastern Florida although they may
have shared a more or less simultaneous inception seem to have differed
greatly in their active life. Thus, at the extreme southern end, the
coastal arc that fronts the Silver Bluff Ridge along Biscayne Bay seems
to have begun as the seaward edge of an arcuate oolite shoal in the
Pamlico Sea while at the north the high ridge in the vicinity of Del Ray
Beach, Boynton Beach and Lantana (P1. 3) exceeds 40 feet in elevation
and was probably a southward extending spit in the Pamlico Sea.
Higher parts of the ridge atop the mainland lagoonal shoreline scarp
between these northern and southern extremes probably were partly
above and partly below the Pamlico Sea level. In general they seem to
have been increasingly below it with distance southward toward the
distal shoal that became the present Silver Bluff Ridge. During later
times of sea levels lower than Pamlico these shoaly bars, islands and
spits were integrated to make shorelines of more continuity which
became derelict at higher than present sea levels at the north and at
present sea level at the south.
There is a good possibility also that the spit-like southward
growth of the barrier was not wholly accomplished in post-Flandrian
time either. Perhaps the more northerly coastal arcs were cut off from
the open sea during the time when the four foot surface at the low coral
keys and the oolite keys was being formed. The lagoons between the
first three mainland coastal arcs and the barrier are increasingly
emergent toward the north with urban development on natural, dry
ground.
Still farther north between Pompano Beach and Boynton Beach
in the general vicinity of Deerfield Beach, Boca Raton and Del Ray




BUREAU OF GEOLOGY


Beach the derelict lagoon is a frankly emergent relict with a floor that
rises gradually westward from an elevation of about five feet immedi-
ately landward of the old barrier to about 25 feet at the toe of the scarp
of the relict mainland shore. The present oceanic shore line here seems
to be situated in about the same place as its predecessor that was made
during the last pre-Flandrian sea level that was higher than present sea
level. Complementarily the barrier is higher here also. North of the
headland at Pompano Beach it commonly exceeds 20 feet elevation,
while south of Pompano Beach it rarely reaches ten feet.


THE MIAMI RIDGE

There is a persistent ridge along the mainland shore of the east
coast of Florida. North of Palm Beach it is a prominent relict beach
ridge, but south of Palm Beach it changes character. Although ridges
persist as far south as Miami; the sand of which they are built gradually
changes its composition with distance southward. North of Palm Beach
it is almost wholly quartz and other detrital minerals but with distance
southward from Palm Beach it acquires steadily increasing percentages
of calcareous oolite. More or less coextensive with this change in
mineralogic composition is a change in topography. As the sand be-
comes more oolitic it takes the form of a relict oolite shoal; a broad low
swell a few miles wide and some ten to fifteen feet high. Toward the
north it is surmounted by several relict beach ridges but their number
decreases southward until they disappear somewhat north of Miami.
This change of form with change in composition seems to reflect
sedimentary process. To the north where the sand is dominantly
detrital quartz it seems to have been moved to its present location by
longshore drift, hence, its characteristic repetitive topographic form is
that of successive beach ridges and swales. Some of these may have
been formed by prograding shorelines. But a general tendency for the
land surface to be higher with distance landward suggests that several
sea levels have been involved; probably there were several discrete
transgressions. These successive beach ridges at different elevations can
be seen in plate 3. Their number diminishes southward by disappear-
ance of the higher ones.

While the older shorelines to the north were building the higher
beach ridges of detrital quartz and coquina, the more southerly parts of
the present Miami Ridge were being deposited as a broad shoal or
shallow submerged bore of calcareous oolite which seems to have
resembled the present Browns Cay on the western side of Andros Bank





GEOLOGICAL BULLETIN NO. 51


in the Bahamas. As Newell (1960b) has shown, such oolite banks
precipitate on shallowly submerged edges of broad shoal areas where
these abut deep water. Tidal overwash fed from the deeper water passes
over the edge of the shoal where warming, pressure reduction, and
agitation cause it to lose carbon dioxide and precipitate calcium
carbonate. The optimum depth for such precipitation seems to be less
than six feet at low tide (Newell, 1960b).
These observations seem pertinent to any attempt to explain the
Miami Ridge for it is located in a place where the same genetic factors
could have worked. It is near the edge of the continental platform at an
elevation that in Pamlico time would have been submerged in shallow
sea water of about the same depth as that which now covers the
Bahaman oolite shoals. It lies to landward from a part of the coast that
is impoverished for beach sand. This is seen in the present absence of
beaches south of Cape Florida. But in Pamlico time the distal part of
the present peninsular mainland was shallowly submerged like the
Bahama Banks and mineral sand doesn't seem to have reached it in
sufficient supply to build any beaches at all in the latitude of the Miami
Ridge. The Miami area was protected against influx of detrital sand by
its remote distal situation just as the Bahama Banks are now protected
against it by their oceanic isolation. Thus, there would have been
unhindered opportunity for a shallow bank to accumulate a mass of
chemical sediment as in the relict oolite shoal of the Miami Ridge or the
presently active ones on the Bahama Banks.
The topography would have tended to concentrate tidal flow in
the Miami area for tidal flows would have entered jet-like on the east
through the relatively narrow opening between the southern end of the
Pamlico-aged barrier beach at the north and the Key Largo coral reef at
the south. But once through this orifice they could have spread broadly
westward across a marine bank (the present Everglades) toward the
Gulf of Mexico.

RELICT MANGROVE ISLANDS

The present topography of the Miami Ridge was acquired during
the process of its emergence from the Pamlico (?) sea. As the water
above the oolite shoal became shallower, mangroves began to establish
themselves tending to form ring-shaped islands like the present ones
along the northern edge of Florida Bay. These last usually have no
names, so I will identify them by the names of the bodies of water they
enclose, as Blackwater sound, Little Blackwater sound, Long Sound,
Manatee Bay, Joe Bay, and Madera Bay. Relicts of the ring-shaped




BUREAU OF GEOLOGY


Figure 23. Fossil mangrove roots showing cylindrical holes where
roots rotted out of encasing oolite

Pamlico islands of the Miami Ridge can be seen in plate 2 which was
condensed from the 71/2 minute topographic maps of the United States
Geological Survey. Despite their inadequate five foot contour interval,
these maps show a line of ring-shaped ridges which I believe are
emerged relicts of mangrove islands somewhat like those of Florida
Bay. They have roughly similar shape and size in plan. However, those
of the Miami Ridge had tidal channels between them (the present
transverse glades) which assured that each ring-shaped island was quite
discrete from its neighbors. But the present mangrove islands of Florida
Bay run together and branch in a braided pattern.
In most instances where these levee-like ring-shaped hills were
examined in exposure they showed external molds of mangrove roots





GEOLOGICAL BULLETIN NO. 51


as their dominant innate structure. Not infrequently these molds are
very detailed preserving the form of a plexus of roots over an extensive
area. The molds are formed of calcareous oolite grains cemented
together. Their characteristic form is that of a hollow tube. The walls of
the tubes vary in thickness. As they become thicker the external
surfaces of the tubes tend to lose their resemblance to mangrove roots.
Differential thickness of cementation makes the outside of the tubes
ragged and irregular. But when tubes are broken through, their internal
surfaces are usually seen to be smoothly cylindrical, true external
molds of the original mangrove roots (Fig. 23).
Where their walls are not unduly thick a plexus of these tubes
looks very much like an intimate intergrowth of mangrove roots (Fig.
24). Such intergrowths can be seen very well in the cut on the west side
of the Sunshine State Parkway (Florida Turnpike) immediately south
of Honey Hill Road (N.W. 199th Street) which is a short distance south
of the northern boundary of Dade County and south of the bridge over
Snake Creek Canal. These tubes branch in the manner of mangrove
roots which have a strong tendency to grow rectangularly in horizontal
and vertical directions. Many of the vertically oriented tubes seem to be
fossil pneumatophores of black mangrove, Avicennia, resembling those
described by Hoffmeister and Multer (1965). Others are fossils of the
geotrophic roots that descend from horizontal ones.
The fossil roots of the relict mangrove islands differ from the
younger ones described by Hoffmeister and Multer from Key Biscayne
which is a part of the present sand barrier. In the instance they describe
the root itself has been variously replaced with calcareous materials and
a layer of sand grains, largely quartz, has been cemented together
around its exterior surface. The resulting entity they refer to as a
"rod". But in the much older, Pamlico (?) deposits of the relict
mangrove islands very little quartz was involved. The enclosing material
was mostly calcareous oolites which seem to have been more volumi-
nously cemented together to form a thick encrusting layer around the
roots. The roots themselves are not usually fossilized. At least I recall
seeing little that resembled the inner layers of the "rods" of Hoff-
meister and Multer (1965). Apparently conditions were not suitable
for replacement of the wood and it rotted out leaving empty tubes
rather than solid rods (Fig. 23).
Hoffmeister and Multer refer to the long standing opinion that
mangroves are rarely fossilized (Bowman, 1917, p. 666). But they also
speculate that "rock structures which are of doubtful origin and which
have tentatively been assigned to worm tubes and burrows of various
animals may actually have originated in some type of marine vegeta-
tion."




BUREAU OF GEOLOGY


Figure 24. Fossil mangrove roots in place in cut on west side of
Sunshine State Parkway

In my opinion the characteristic structure of the Miami oolite
where it composes the relict mangrove islands is that of a plexus of
fossil mangrove roots; mostly external molds made of aglutinated
oolite grains. In some instances the vegetal origin of the form of these
tubular structures is patent, as may be seen in figure 24. But in most
instances the tubes form such a dense snarl that their relation to any
systematic arrangement of the roots of a plant is obscure (Fig. 25). This
complexity probably results from the roots of many generations of
plants as well as various animal burrows penetrating the same space.
Nonetheless, close examination of most exposures of Miami
oolite in the ring-shaped ridges shows rough surfaces with many small
holes. Most of these are an inch or so across. They readily fall into two
categories: (1) irregular shaped holes that are places where loose grains





GEOLOGICAL BULLETIN NO. 51


Figure 25. Cut along sidewalk of N.W. 75th Street, Miami, just east of
St. Mary's Cathedral showing a snarl of fossil mangrove
roots and associated structures in ring-shaped ridge of
relict mangrove island

of oolite have fallen out from between the external surfaces of the
tubular molds of the old mangrove roots, and (2) cylindrical or tubular
holes that are the internal space whence the roots rotted from the
molds.
This kind of structure was found in the oolite at every exposure I
visited in the ring-shaped ridges or relict mangrove islands. Other kinds
of structure appear in these areas too, most notably, thin bedding and
animal burrows but the external-root-mold structure is the commonest
one.
East of the relict mangrove islands, and occasionally truncating
them on the east, is a prominent ridge (the Silver Bluff Ridge) built of




BUREAU OF GEOLOGY


Figure 26. Cut in west side of Sunshine State Parkway (Florida
Turnpile) at Honey Hill Road (N.W. 199th St.), showing
ring-shaped ridge of relict mangrove island

oolite along the Silver Bluff. Superficially, it resembles the ring-shaped
ridges of the relict mangrove islands but on the map it is seen to have
the plan of a high energy oceanic shoreline. The Silver Bluff Scarp is cut
into its eastern edge.
In this surficially indurated oolitic ridge I don't recall seeing any
of the mangrove-root structures. All the exposures I recall showed cross
bedding like that seen at the type locality of the Silver Bluff shoreline
on South Bay Shore Drive in the Silver Bluff section of Miami. This
restriction of the mangrove-root structures and associated fossil bur-
rows to the relict low-energy localities of the ring-shaped ridges and
their absence from the surf-dominated Silver Bluff Ridge suggests that;
the mangrove root external mold is the proper interpretation of the






GEOLOGICAL BULLETIN NO. 51


Figure 27. View eastward along N.W. 75th Street, Miami from a
position near St. Mary's Cathedral. View looks down
eastern edge of ring-shaped ridge formed by relict man-
grove island
structure commonly seen in the relict mangrove islands or ring-shaped
ridges.
The ring-shaped ridges of the relict mangrove islands and the
higher parts of the Silver Bluff Ridge share the highest elevations of
greater Miami. The site mentioned above where Honey Hill Road or
N.W. 199th Street crosses the Sunshine State Parkway is impressive,
although atypical in containing more cross bedding than fossil man-
grove root structures. The road cut where the parkway passes through
the ring-shaped ridge is deep enough to let Honey Hill Road cross it on
an overpass without necessity for fill to maintain clearance in the
parkway beneath. Figure 26 shows the stature of the ridge where it is
transected by the parkway.




BUREAU OF GEOLOGY


Although this is an extreme instance of the local relief produced
by the relict mangrove islands most of the others are steep and high
enough to demand cuts in roads or railroads that cross them. Abrupt
changes in elevation and slope can be seen in figure 28, a view from a
position just east of St. Mary's Cathedral looking eastward along the
south side of N.W. 75th Street toward N. Miami Avenue. Mangrove
root molds shown in figure 25 are located in the road cut seen on the
right in figure 27. Similar structures in another part of the same relict
mangrove island can be seen on the south side of N.E. 69th Street
between N. Miami Avenue and N.E. 2nd Avenue.
About a quarter mile west of U.S. Highway 441 in the NE quarter
of Section 13, Township 50 S.; Range 41 E in the latitude of Fort
Lauderdale, a former rock pit (now used as a playground) shows relict
mangrove roots to advantage. As can be seen on the Fort Lauderdale
South quadrangle, this pit is in an isolated area of continuous high
ground rather than a ring-shaped ridge with enclosed lower ground.
This hill seems to have been a mangrove island like many of those
presently found in Florida Bay that are more or less equidinensional
rather than ring-shaped. It held no lagoon-like body of water in its
center, nonetheless, like the ring-shaped ridges its dominant structure is
that of tubular molds of mangrove roots. Those shown in figure 28
were washed out of incoherent oolite sand from the southeastern wall
of this pit.
Southwestward from the center of Miami, mangrove root struc-
tures can be seen in a prominent ring-shaped ridge that is bisected along
an east-west line by Miller Drive (SW 56th Street). Its eastern edge lies
immediately west of the Palmetto Expressway (Florida Highway 826).
Root structures can be seen where the Seaboard Airline Railroad
transects it both in a low cut at the southwest where it crosses Galloway
Road (S.W. 87th Avenue) and, in a deeper cut west of the railroad
about 1000 feet northeastward from Miller Road. In this last cut,
which is some ten feet deep, cross-bedding dominates the bottom of
the exposure and mangrove root structures are common at the top.

Farther to the southwest, toward the end of the zone of ring-
shaped ridges, the town of Perrine centers in the area enclosed within a
ring that is some two miles in diameter. Near the north edge of Perrine a
small roadside park centers on an old borrow pit on the east side of U.S.
Highway 1 about 1000 feet north of the place where it becomes a
divided highway. The upper two or three feet of the wall of this pit is
dominated by fossil root structures. The lower part of the wall shows
cross-bedded oolite but no root structures.




GEOLOGICAL BULLETIN NO. 51


E(F *- 21


Figure 28. Tubular molds of mangrove roots washed out of Miami
oolite from walls of playground in old rock pit in Fort
Lauderdale

Southeastward from this old pit the ring follows the land enclosed
within the fifteen foot contour as shown on the Perrine 7V2 minute
quadrangle. There are a number of road cuts on residential streets in
this area. Most of them show fossil root structures. A good exposure
may be seen on S.W. 176th Street between S.W. 90th and 91st
Avenues.
The stature and plan of most of the ring-shaped ridges or relict
mangrove islands can be seen on plate 2 where the three intervals
between the 10, 15, 20, and 25 foot contours have been shaded. With
very few and minor exceptions these are the highest elevations' of the
greater Miami area. Their configuration on the maps outlines the




BUREAU OF GEOLOGY


ring-shaped ridges in a general way. But I think a smaller contour
interval would show the ridges to have greater continuity.
It is notable (P1. 2) that no streams transect ring-shaped ridges.
The ridges enclose low ground, but no streams flow through it. Instead
the drainage is concentrated in the areas between ring-shaped ridges in
the valleys that have been known as "Transverse Glades". From north
to south these are the valleys of New River, the natural valleys now
drained artificially by Snake Creek Canal, Royal Glades Canal, and
Biscayne Opaloka Canal, the valleys of Little River and Miami River,
and the valleys now occupied by Coral Gables Canal, and Snapper
Creek Canal. All these drainages thread their way between ring-shaped
ridges and never invade the lowlands enclosed by the ridges.
This supports the idea that the present drainage ways are relicts of
tidal channels that separated the original ring-shaped mangrove islands
before they were rendered derelict by falling sea level.


THE EVERGLADES

Most of the soluble parts of the surface of south Florida have
elevations very close to present sea level. This probably means that
either sea level has returned almost exactly to interglacial levels to
which solution had lowered and deposition raised the carbonate areas,
or solution has lowered these areas to present sea level in post-Flan-
drian time. Most of this low, solution-levelled surface is the Everglades.
Peat overlies the limestone throughout most of the Everglades.
The basal part of the peat has been dated by carbon 14 at about 4,000
years B.P. at a number of places: south' of Lake Okeechobee (Schroe-
der, Klein, and Hoy 1958); along Levee 67 southwest of Andytown
(dates obtained for this study); and near the mouth of the Everglades
Sloughs (Spackman, Scholl, and Taft, 1964). The uniformity of these
dates at about 4,000 years B.P. suggests that the present carbonate
lowlands were low enough to bring a water table to the surface of the
ground and produce swamp conditions when the Flandrian trans-
gression crested. This suggests that the bedrock surface was already low
4,000 years ago and makes it difficult to assume that it was cut down
by post-Flandrian solution engendered by crest-of-Flandrian water
table rise.
Another alternative is to assume that the solution took place over
a longer period of time and most actively during lower glacial sea levels.
This, of course, raises the problem of explaining the absence of solution
depressions whose surfaces are lower than present sea level. Perhaps





GEOLOGICAL BULLETIN NO. 51


they may exist in the person of the sub-sea level parts of the low places
that hold Florida Bay, Biscayne Bay, and Lake Okeechobee. But such
sub-sea level areas are not impressive. They are few and they reach
depths only a few feet below sea level. And these low areas are more
plausibly explained by other means. Moreover, solution during lower
sea levels could not produce a plane surface so nicely adjusted to
present sea level as the Everglades. Carbonate deposition could produce
a flat surface and undoubtedly has helped to maintain and repair the
extant one. But the extant surface of South Florida is dominantly
micro-karst which bespeaks an origin by lowering to a base level rather
than by building up to one.
The problem suggests the repetitive return of the sea essentially to
its present level during several interglacials as suggested by the work of
Parker and Cooke, (1944), Alt and Brooks, (1965), and others outside
of Florida. The solution produced during each of these repetitively
duplicated interglacial high sea levels would help to lower more of the
carbonate land surface to elevations little above this recurrent sea level.
Meanwhile, peat would grow on already lowered parts of the land
surface and preserve them against further lowering. Thus, the Big
Cypress, Everglades Keys, and Miami Ridge are now being lowered by
solution while the Everglades is protected against further lowering by
its covering of peat. However, such protecting peats probably disappear
quickly when sea level falls during glacial times.
A critical factor in determining where fibrous peat accumulates in
south Florida seems to be the nature of the base on which it rests. It
commonly lies on limestone and rarely on silica sand. This association
of fibrous peat with a limey base supports the concept of an Everglades
Trough cut down by solution. Apparently the fibrous peat accumulates
on the limestone because the limestone can be dissolved down to
watertable. The resulting poccosin creates the swampy condition nec-
essary for the growth of fibrous swamp plants and their preservation as
peat. The surface of silica sand can not be so readily reduced to a
poccosin because it is not lowered by solution except for reduction of
volume as its shell component is leached out.
A widespread blanket of peat such as that of the Everglades
Trough overlying a karst surface induces speculation that the solution
was effected by organic acids drained out of the peat. There seems little
reason to believe this has happened. Dr. David Alt (personal communi-
cation) could find no acid water coming from the peat. Moreover, the
topography of the limestone surface buried beneath the peat of the
Everglades near levee number 67 of the Central and South Florida
Flood Control District is essentially similar to that of the exposed




BUREAU OF GEOLOGY


limestone surface at Pinelands Trail on the Flamingo Highway in the
Everglades National Park.
The topographic maps shown in figures 3, 29 and 30, show
micro-karst in these two places. The two maps shown in figures 3 and
29 were made by contouring elevations obtained from a one foot grid
over areas 10 feet square. Figure 30 used a ten foot grid over an area
100 feet square. The map of the area near Pinelands Trail (Fig. 3) was
made directly from the subaerially exposed surface of the limestone.
The maps of the limestone floor beneath the peat of the Everglades
(Figs. 29 and 30) were made from information obtained by probing to
hard rock with a 3/8 inch steel rod at a location about 100 yards south
of Levee 67 and about two miles west of U.S. Highway 27.
The topography shown on all three of these maps is so similar it
suggests both surfaces were made in the same manner. Since the
Pinelands Trail area is dry enough to support an open pine forest, it
seems doubtful that it was ever covered by post-Flandrian peat. This in
turn, suggests that the similar surface at Levee 67 was made under
similar conditions of subaerial exposure before the peat began to
accumulate.
The artesian head in the Biscayne aquifer (Schroeder, Klein, and
Hoy, 1958) is normally great enough to maintain a piezometric surface
higher than the land surface through most of the Everglades. In the
absence of a continuous cap rock this also casts doubt on the validity of
explaining the karst surface beneath the peat by water that decended
through the peat deriving acid from it.
The presence of an artesian aquifer below the Everglades also
raises the possibility that the surface has been lowered by solution
effected by moving artesian water. This also seems a small possibility
for several reasons. The karstic surface is obviously the product of
solution at the surface of the limestone, and artesian water would not
fit its movement to the contact between the peat and the limestone. It
would more plausibly spread its flow through a thick zone of perme-
able rock. Any solution produced by such a thick zone of flow would
cause broad, gently sloping topographic sags or big, steep-walled col-
lapse sinks rather than minutely and intricately etched surficial micro-
karst at the interface between limestone and peat.

At the base of cores of the unconsolidated stuff overlying the
limestone there is a thin, white stratum a few inches thick that usually
is silt and fine sand resting directly on the top of the limestone and
overlain directly by the peat. Davis (1946) referred to this as the Lake
Flirt Marl, but here, at least, it is mostly insoluble. If the karst surface





GEOLOGICAL BULLETIN NO. 51


2$


N

0 2 3 4 Feet.
Approx. Scale


Figure 29 Contours on surface of limestone beneath peat in Ever-
glades alongside Levee 67 about one mile west of U. S.
Highway 27, one foot grid


~~\3 2/




BUREAU OF GEOLOGY


of the limestone directly beneath were the product of sagging or
collapse caused by solution throughout a thick vertical zone, this
insoluble residue should also be distributed throughout the vertical
zone in which the solution occurred. On the other hand, its presence as
a thin, sharply defined septum between limestone below and peat
above suggests that it was originally a soil developed subaerially on the
limestone when it was exposed at the surface of the ground under
conditions of good drainage in pre-Flandrian time. This idea is sup-
ported by the presence of soils formed of similar insoluble residues
along the Tamiami Trail on limestone in parts of the Big Cypress where
the surface is usually dry.


DEPOSITION AROUND THE EDGE OF THE EVERGLADES

Although the limestone surface of the Everglades Trough has been
lowered by solution, there is little doubt that deposition along its edges
has helped to confine it as an axial drainage way. Quartz sand moved
southeastward from both east and west coasts of the peninsula in
Pamlico time, but did not enter the Everglades. It built the sandy
Immokalee Rise west of the Everglades Trough and much of the
Atlantic Coastal Ridge east of the Everglades.
The protection of the Everglades Trough against incursions of
southeastward-moving quartz sand is involved with the prior develop-
ment of the Kissimmee Valley up-peninsula to the northwest. The
Okeechobee Scarp extends from the south end of the Indiantown
Ridge on the east, around the north side of Lake Okeechobee, to the
south end of the Lake Wales Ridge (P1. 1). It is an erosional scarp with a
level base and a crest of differential elevation. This assures that it is
younger than the Kissimmee River Valley which it truncates at the
south.
The Kissimmee River Valley is a broad, open, gently sloping swale
some 20 miles wide which extends in length from the cross-peninsular
divide at the head of the Kissimmee River to the Okeechobee Scarp
immediately north of Lake Okeechobee, a distance of some 75 miles.
This valley was formed by solution-sagging or subsidence of its surface
by subterranean solution without complete destruction of its original
surface details. Thus, the drainage pattern of the Kissimmee River and
Taylor Creek shows their consequence to relict beach ridges that were
built along a succession of Atlantic shorelines as the sea regressed
eastward across this area. These relict beach ridges are but meagerly
suggested in the lower parts of the Kissimmee Valley, but they become
clearer with distance up the side slope of the valley toward the east.





GEOLOGICAL BULLETIN NO. 51


N
0 10 20 30 40 Feet

Approx. Scale









Figure 30 Contours on surface of limestone beneath peat in Ever-
glades alongside Levee 67 about one mile west of U. S.
Highway 27, 10 foot grid




BUREAU OF GEOLOGY


Since they are relicts of Atlantic Oceanic shorelines and become higher
in the direction of the present coast, obviously the more westerly ones
must have been lowered since they emerged (White, 1958, and discus-
sion of Osceola Plain in this report). These relict beach ridges are
closely parallel with modern Atlantic oceanic shorelines and also with
other relict shorelines at elevations both higher and lower and locations
both east and west of the present Kissimmee Valley. They assure that
the Atlantic regressed eastward across the area now occupied by the
Kissimmee Valley leaving a series of relict shorelines that were all
essentially straight, and parallel with the present Atlantic beach.
The Atlantic shoreline must have regressed from these relict beach
ridges before the Kissimmee Valley acquired its present trough-like
character and while its surface was still inclined gently eastward toward
the Atlantic with a continuous slope from the eastern toe of the Lake
Wales Ridge to the crest of the east-facing scarp that bounds the
Osceola Plain on the east. Any quartz sand drifted southward into the
area now occupied by the Everglades Trough from these relict beach
ridges of the present Kissimmee Valley must have been delivered before
the valley was formed by sagging of the original eastward-sloping beach
ridge plain. The level toe and differential crest elevation of the Okee-
chobee scarp assure that the Kissimmee Valley had sagged before the
scarp truncated it. There is no trace of such sand on the surface of the
Everglades Trough now. Possibly the surface on which it was deposited
has been dropped by faulting and buried by younger, lower energy,
calcareous sediments such as the Fort Thompson formation.
Faulting is suggested by a number of features along the line that
separates the low distal part of the peninsula from its higher central
part. A major topographic break occurs here. It includes the narrowing
of the peninsula south of Sanibel Island on the west coast, the course of
the Caloosahatchee River, and the straight northwest shore of Lake
Okeechobee. It terminates the higher ground to the north in the
southern end of the DeSoto plain which is some 60 feet high at the crest
of the Caloosahatchee Incline north of the Caloosahatchee Valley
compared with elevations generally half that high in the Immokalee
Rise to the south. It truncates the Lake Wales Ridge. And the Okee-
chobee scarp seems to have been eroded back to its present location as
the shoreline of a sea (Pamlico ?) that once existed to the south
submerging the distal part of the peninsula south of the Kissimmee
Valley. Also this line generally separates quartzose sandy soils on the
north from peats overlying limestone on the south.
Tanner (1965) has suggested a fault here. It would be parallel with
the one mapped by Jordan, Malloy, and Kofoed (1964) along the




GEOLOGICAL BULLETIN NO. 51


northern side of the Pourtales submarine terrace south of the Florida
Keys and would also be parallel with the fault suggested by Vernon,
(1951), and White, (1958), which ends the Kissimmee faulted flexure
at its southern end in the latitude of Cape Kennedy.
Both the subsidence that formed the Kissimmee Valley from the
former beach ridge plain and any down-faulting of the former exten-
sion of this valley must have antedated the sea level (Pamlico ?) at
which the Okeechobee scarp was made. Thus, (Pamlico ?) sand could
be drifted into positions southeast of the Caloosahatchee River-Lake
Okeechobee lineament only in places that were in line with the (Pam-
lico ?) oceanic beaches of the east and west coasts of the peninsula to
the north. These were located near the present east and west coasts of
the Peninsula and accordingly the Pamlico quartz sand south of the
lineament is all near the edges of the peninsula as seen in the Atlantic
Coastal Ridge (northern part of the Miami Ridge) along the east coast
and Immokalee Rise on the west coast. Between these two peripheral
ridges of quartz sand is the sand-free Everglades Trough.


INFLUENCE OF STRUCTURAL LINEAMENTS ON SOLUTION
IN THE DISTAL ZONE OF THE PENINSULA

Throughout the Florida peninsula confusion arises in recognizing
structural lineaments because one of their two principal trends (Ver-
non, 1951, figure 11) is the same as the relict and present oceanic
shorelines of the east coast. This complicates what has been said about
the Everglades in the immediately foregoing part of this report because
differential solution at depth on opposite sides of structural lineaments
may have determined geographic boundaries between overlying, thin
Pleistocene formations. The boundaries between the confining Pamlico
(?) quartz sands southwest and northeast of the Everglades Trough and
the Fort Thompson formation which floors the trough have this dually
explicable orientation.
The geologic map of the distal end of the Florida Peninsula
presented by Schroeder Klein and Hoy (1958) is reproduced here in
simplified form as figure 31. It will be noted that most of the contacts
between formations follow lineaments of one or the other of the two
main sets. I have added peripheral arrows on the edge of the map to
mark these lineament-founded formational contacts. One of these (the
one pointed out by the arrows numbered a and a') lies along the
northeast-southwest lineament mentioned in the immediately preceed-
ing section that locates the southeastern end of the Central Highland




BUREAU OF GEOLOGY


section of the Florida peninsula, the cape at Sanibel Island, the valley
of the Caloosahatchee River, and the northwest shore of Lake Okee-
chobee. It brings the Anastasia formation into contact with the Fort
Thompson and Tamiami formations. Parallel with it, farther to the
southeast, another major lineament, marked by the peripheral arrows b
and b', brings four different formations into contact; the Tamiami
formation against the Anastasia, the Fort Thompson against the Miami,
and the Miami against the Anastasia. With the exception of the Miocene
Tamiami formation these are all Pleistocene formations that are fre-
quently referred to as contemporaneous in part (Parker and Cooke,
1944: Cooke, 1945; Schroeder, Klein, and Hoy, 1958; Puri and Ver-
non, 1959.) There is little reason to think that most of these young
formations were ever buried under any appreciable sedimentary cover,
and their common surface is nearly reliefless. Hence it is difficult to
think of the structurally controlled boundaries between them as pro-
duced either by faulting that broke them or by differential reduction
after such fault breaking. More plausible is the possibility that the
surface on which these Pleistocene formations were deposited had
acquired a fault-controlled topography before they were laid down.
This could have been by differential solution of the pre-deposition
surface or by differential subsidence of this surface because of solution
at greater depth. In this connection it is of interest that Schroeder and
Klein (1954) regarded all the contacts of their area of study in the
western Everglades and eastern Big Cypress as unconformable.
The difference in sedimentary environment made by different
water depths on opposite sides of lineaments that juxtaposed buried
formations of different vulnerability to solution would form the
boundaries between topographically low areas on the more soluble
rocks and higher areas on the less soluble rocks. Submerged shallowly
beneath an interglacial sea (Pamlico ?) the topographic relief so pro-
duced would affect water depth and therefore the kind of sediment
accumulated in it.

Such initial topographic differences may partly account for the
distribution of such differing Pleistocene formations as the Anastasia,
the Miami and the Fort Thompson, which in turn, are largely responsi-
ble for the present topography of the distal end of the Florida penin-
sula. In a broad, shallow submergence like that now extant on the
Bahama Banks, peripheral places produced the Anastasia formation
where wave energy was high. Where tidal overwash by straits water was
great and wave energy less the oolite was precipitated. And between the
peripheral barriers so built, the Fort Thompson formation was de-
posited in the central (Everglades) trough in water that was sometimes




GEOLOGICAL BULLETIN NO. 51


-----------






Miami Oolite

] Anastasia formation Z

R Key Largo Limestone

Fort Thompson formation

6.. Caloosahatchee Marl

IU Tamiami formation






Figure 31 Geology of the Distal Zone of the Florida Peninsula. After
Schroeder, Klein and Hoy (1958)




BUREAU OF GEOLOGY


salt and sometimes fresh depending largely on the depth of sub-
mergence.
Unlike the present situation in the Bahama Banks, voluminous
fresh water enters the central trough of the distal part of the Florida
peninsula from the discharges of south-flowing rivers of the central part
of the peninsula, Fisheating Creek, the Kissimmee River, and Taylor
Creek. This water-freshening influence probably helped to form the
fresh water faces of the Fort Thompson Formation. Much of this
facies may have been deposited where salt water and fresh water
mingled as they do now at the inner edge of the mangrove zone along
the southwestern mainland coast of the peninsula.


LAKES AROUND THE EDGE
OF THE EVERGLADES TROUGH

The edge of the Everglades Trough is marked by a zone of extant
and relict lakes. They seem to have come into existence as small lakes
located along the edge of the peripheral quartz sand since the aquatic
peat which accumulated in them reaches its lowest elevations there. As
they became filled with aquatic peat they were increasingly overlapped
by sawgrass fibrous peat.
Along the southwestern edge of the Everglades Trough many
small lakes mark the edge of the bordering higher area of quartz sand
that forms the Immokalee Rise. The large Lake Hicpochee is in an
essentially similar position near the western corner of the Everglades
Trough, and the largest of all Florida lakes, Lake Okeechobee, domi-
nates the northwestern end of the trough extending nearly all the way
across it. In general, the more northwesterly parts of the shoreline of
Lake Okeechobee are founded on quartz sand while the southeastern
parts show peat resting directly on limestone. On the northeastern
flank of the Everglades Trough were the Hillsborough Lakes and
Loxahatchee slough, now largely drained. They were founded on the
southwestern edge of the quartz sand of the Atlantic Coastal Ridge.
The relation between the deepest parts of these lakes and sand-
coated limestone suggests that the lakes first came into existence
through the same process that formed the basins of lakes farther up the
peninsula to the north that occur in similar stratigraphic situations in
which quartz sand overlies limestone; especially along the toes of scarps
(White, 1958).
Apparently these lakes on the periphery of the Everglades Trough
came into existence with the rise of water table that accompanied the





GEOLOGICAL BULLETIN NO. 51


cresting of the Flandrian transgression when the sea rose to its present
level, only a few feet lower than the surface of the Everglades. The
surface of the limestone was lowered by solution where accelerated
discharges of ground water emerged from the sand at the toe of the
peripheral scarp of the Everglades. From the nuclei of these small
peripheral sag ponds larger lakes developed as the fibrous peat of the
Everglades thickened with time to become a rising dam. These widened
lakes became additions to the Everglades Trough enabling it to increase
in width with the passage of post-Flandrian time. The progress of this
surface-lowering and trough-widening is shown by the distribution of
aquatic peat (Loxahatchee Peat). Figure 32 after Davis (1946) shows
variation in thickness of the peat in the Everglades Trough. It is thickest
around the edge of the trough. From the vertical cross section shown in
figure 33, also after Davis, it can be seen that this thicker peripheral
part of the peat is Loxahatchee aquatic peat, a sapropel accumulated in
lakes. Furthermore, it is thickest where the underlying rock floor is
lowest, and this lowest zone is at the extreme edge of the peripheral
sand. This seems to show that the surface of the limestone was lowered
by solution where it was overlain by the sand, which widened both the
Everglades Trough and its covering of peat. Apparently the sawgrass
peat began to accumulate in the center of the Everglades Trough and
spread laterally over the earlier formed Loxahatchee aquatic peat as the
peripheral lakes became derelict by being increasingly filled with
aquatic peat. Through this process the Everglades Trough seems to have
widened itself by invading the solution-lowered edges of t! peripheral
sand-covered areas.
These peripheral lakes have been enlarged by having their outlets
raised. By this process Lake Okeechobee became the largest lake in
Florida. If it existed at the crest of the Flandrian transgression 4,000
years ago it was probably much smaller. Under natural conditions,
before the present drainage works and dikes were made, it overflowed
its southeastern and southwestern banks at an elevation of some 18
feet, to discharge water into the Everglades Trough and the Caloosahat-
chee Valley. At that time the peat in the Everglades Trough adjacent to
the southeastern shore of the lake was about eleven feet thick. As the
peat thickened with the passage of post-Flandrian time, the surfaces of
both the peat and the lake dammed by it rose until they were eleven
feet higher than they were at the crest of the Flandrian transgression
when the peat first began to accumulate. It was this rise of surface level
that allowed Lake Okeechobee to spread its waters broadly across the
surrounding lowlands to become the biggest of Florida's lakes.
Davis's profiles of the Everglades Trough (Fig. 33) suggest that the
former lakes along its northeast and southwest edges migrated away




BUREAU OF GEOLOGY


LAKE
LEGEND OKEECHOBEE
OKEECHOB
MUCK
PEAT
THICKNESS
FEET








MIAMI



WITHIN LIMITS ,
OF EVERGLADES


MANGROVE
PEAT


ISO
SHOWING THI
THE


PA
CKN
EV


C H
ESS
ERG


MAP
OF PEAT
LADES


Figure 32 Isopach map of the Everglades region showing thickness of
peat and some muck areas











/ HARD FRESH-WATER LIMESTONE
C A LOOSAHATCS MRINHE _SIALL ED
C A LOOSAHATCH E E ---_ HARD FRESH- WATER LIMESTONE
U&RINF $HFI I BED


MARL


T A M IAMI


ORIGINAL POF TREE ISLANDS
S: PEAT


A 0 FE' H-wATE., I,.I T.'.rIE -
HARDN SHEL A. NASTASIA
MARIN SHELL BE FORMATION
HARD FRESH-WATER LIMESTONE
MA "R-I NE SHELL BED


FO R M


A T I N


Figure 33 Profile across the Everglades showing layers of peat and
some marl, rock, and sand sediments


L E G E N D HOR. SCALE '2MILE
C COM PACT PEAT rTI PAMLICOSAND LAKE FLIRT MARL
SAW-GRASS PEAT I GANDY PEAT I LOXAHATCHEE PEAT


--


I


1




BUREAU OF GEOLOGY


from the axis of the Everglades Trough, encroaching on the walls of the
trough as a rising dam of sawgrass peat in the center of the trough
progressively raised the levels of their water surfaces and overlapped
the earlier formed aquatic peat. The smaller of these peripheral lakes, as
they grew wider, acquired a fill of Loxahatchee aquatic peat and thereby
widened the Everglades by enabling both aquatic and fibrous peat to
extend across the edge of the peripheral quartz sand of the adjacent
Miami Ridge to the northeast and Immokalee Rise to the southwest.
The larger Lake Okeechobee acquired less aquatic peat and acquired
wider and wider expanses of open water as its surface rose behind a
rising dam of fibrous peat.
Further evidence for the idea that the Everglades Trough has been
widened by lake-forming solution of limestone beneath a covering
blanket of quartz sand may be had from the change in the eastern edge
of the Everglades Trough farther south, where the overlying quartz
sand is replaced by the Miami oolite. At the north, where the trough is
bounded by quartz sand, its peripheral slope is steep, its peat burden
thicker, and its sub-peat floor lower. Farther south, and farther down
the drainage direction, where the trough is bounded by the soluble
calcareous oolite of the Miami Ridge, its peripheral slope is gentler, it
has no peripheral lake basins, and its sub-peat floor is higher.

REASONS FOR DIFFERENT KINDS OF
SWAMPY SURFACE IN THE DISTAL ZONE

The low, swampy, lime-founded areas of the distal part of the
Florida peninsula have three kinds of surface whose distribution seems
to be determined by the nature of surface drainage.
(1) Where drainage is more or less confined by peripheral areas of
higher ground, the surface tends to grow up with peat. This is best seen
in the Everglades Trough. It is a great swamp throughout its whole
extent. Its drainage is confined between areas of higher ground; the
Atlantic Coastal Ridge (Miami Ridge) to the east and southeast, and the
Immokalee Rise and Big Cypress to the southwest. In general, the flow
of surface water is confluent toward the somewhat restricted outlet of
the Everglades Sloughs at the southwest.
(2) Where drainage is more diffluent or centrifugal, the surface
has no cover of peat and is mostly bare pre-Flandrian limestone as in
the Big Cypress or on the southwestern extension of the Miami Ridge
between Homestead and Whitewater Bay. Both of these are places
where, under natural conditions, water from the Everglades Trough
overtopped the peripheral divide and escaped its confinement to spread




GEOLOGICAL BULLETIN NO. 51


diffluently outward toward the sea. In the case of the Big Cypress much
of the water came from the Immokalee Rise to the north.
(3) Such low, swampy areas of bare limestone give way to
hinter-coastal zones where lime mud accumulates, as on most of the
mainland shore of Florida Bay and the Gulf of Mexico between
Homestead and Cape Romano except behind Cape Sable and the
mouths of the Everglades Sloughs.
The reasons for these three different kinds of low swampy sur-
faces are not wholly clear; but their relation to the drainage conditions
described seems fairly certain.
The growth of peat in areas of convergent drainage may result
from the persistence of swampy conditions in such places. By contrast,
the diffluent drainage of peripheral divides such as the Big Cypress and
the southwestern extension of the Miami Ridge offer less restriction to
flow of swamp water and allow it to flow away completely in times of
drought. This might be inimical to the growth of the swamp vegetation
that builds up the peat. Or, perhaps more plausibly, such dry periods
allow peat to oxidize or burn. Davis (1946) describes fires that have
removed thin layers of peat from areas peripheral to the Everglades
Trough. But the fires he refers to post-date construction of the major
drainage canals of the southeastern part of the peninsula, and the drier
conditions that enabled the peat to bum may have come from an
artificially lowered water table.
The hinter-coastal areas of the third zone where lime mud accu-
mulates are more difficult to explain. Their drainage has been described
above in the section entitled Florida Bay. They are continuous from
the mainland shore of the sea to the seaward edge of the second zone
where bare pre-Flandrian limestone is exposed. This lime mud is
usually called marl. Near the sea it has been called marine marl. Toward
its landward edge it has been called fresh-water marl. This distinction
seems to have been based on differences in the relicts of flora and fauna
it contains. But the process which made the marl seems to be the same
throughout its whole extent for it is a continuum which stops equally
abruptly at the edge of the second zone of bare pre-Flandrian limestone
on its landward edge and at the shore of open lagoonal water on its
seaward edge. It persists landward as far as scrub mangrove does and no
farther. This relation between mangrove and lime mud can be seen
along the Flamingo Road (Florida Highway No. 27) in the Everglades
National Park. The dwarf cypress and karstic surface of bare pre-
Flandrian limestone end together at the extreme landward edge of the
scrub mangrove zone where the pre-Flandrian limestone begins to be
buried under the feather edge of the lime mud.




BUREAU OF GEOLOGY


Since the mangrove is a littoral plant I tend to think that both the
mangrove and the lime mud are dependent upon the influence of salt
water, although Davis (1940) says mangrove roots penetrate rock
ledges only with difficulty. Possibly precipitation of lime mud in such
places may be brought about by mixing lime-laden fresh water with
marine salt water in a somewhat similar manner to that described by
Russell (1962) in his discussion of beach rock.
Solution pits are everywhere throughout the bare surface of
pre-Flandrian limestone as seen in the dwarf cypress area of the
diffluent second zone. They stand full of water even during times of
drought. They don't fill up with lime mud, but rather are refuge for
aquatic animals. They so frequently harbor alligators that they are
commonly called alligator holes. A few hundred yards seaward from
the outermost of these fresh-water-filled solution pits of the second or
bare limestone zone, the most landward outposts of scrub mangrove
are rooted in similar solution pits that are filled with lime mud.
"Lime Levees" were described by Spackman, Scholl and Taft
(1964). These deposits of lime mud border tidal channels that pene-
trate the peat-covered areas of the southwestern coast of the peninsula
in the area of Whitewater Bay and the Everglades Sloughs. I think they
are another instance of the deposition of lime mud where fresh and salt
water mingle.
I have found little to suggest the occurrence of true fresh water
limestone in south Florida. Most Florida lakes tend to have bottoms
foul with carbonaceous matter, sapropel or aquatic peat. Their bottom
waters are commonly foul with hydrogen sulfide. They don't provide
environments favorable to accumulation of limestone by either bio-
logic or physico-chemical means. The Lake Flirt "marl" has always
been mapped as a fresh water marl but elsewhere in this report I offer
evidence that where it underlies the Everglades peat it is largely an
insoluble residue from pre-Flandrian solution of the limestone that
underlies the peat.

THE IMMOKALEE RISE

In the northwestern part of the Distal Zone of the Florida
Peninsula the Immokalee Rise lies north of the Big Cypress, west of the
Everglades and south of the Caloosahatchee Valley. Like the Atlantic
Coastal Ridge south of West Palm Beach, it is a southerly extension of
Pamlico (?) marine sand invading the Distal Zone from the sand-
dominated Central Zone to the north. Unlike the Atlantic Coastal
Ridge, however, the Immokalee Rise shows few relicts of Pamlico





GEOLOGICAL BULLETIN NO. 51


shoreline features. It seems to have been built in Pamlico time as a
submarine shoal that extended southward from a mainland cape at the
south end of the Desoto Plain much in the manner that the present
off-cape shoal extends southward from Cape Romano. Fahkahatchee
and Ocaloacoochee Sloughs seem to be emergent relicts of Pamlico
tidal passages through this shoal. Relict coastal features that may have
formed during emergence of the shoal from the Pamlico sea are very
weakly developed. Apparently low energy conditions prevailed and
prevented the development of prominent shoreline features.
As in other areas where sand overlies limestone, (White, 1958) a
line of lakes has developed along the feather edge of the sand-covered
area, to the extent that the sandy Immokalee Rise is ringed with small
solution lakes. The occurrence of these peripheral lakes is so character-
istic that the edge of the sand-covered area can be delineated by
drawing a line on the map connecting the lakes.



THE MIDPENINSULAR ZONE
THE ATLANTIC COASTAL LOWLANDS


ATLANTIC COASTAL RIDGE, LAGOONS AND BARRIER CHAIN

With occasional interruptions the Atlantic Coastal Ridge extends
along the mainland coast of the Florida Peninsula from the south shore
of the St. Mary's River at the Georgia State boundary to the vicinity of
Homestead some 30 miles southwest of Miami in Dade County. It is
made of relict beach ridges and bars sometimes single and sometimes
multiple.
North of Eau Gallie in Brevard County the ridge is generally wider
than it is from Eau Gallie southward, but it ividens again to maximal
dimension near its southern end in Broward and Dade counties in the
vicinity of Fort Lauderdale, Miami, and Homestead. The narrower part
of the ridge south of Eau Gallie is generally located closely along the
mainland shore with the Indian River or equivalent lagoon directly at
its eastern toe, save for the stretch between Sebastian in Indian River
County and Fort Pierce in St. Lucie County where lower ground
intervenes between the ridge and the shore. This suggests that it
involves the last mainland oceanic shore to be formed. North of Eau
Gallie on the other hand the ridge is not only broader but usually sits
back some mile or so from the mainland shore of the lagoon.




BUREAU OF GEOLOGY


This appearance of greater antiquity is increased north of the
Volusia-Brevard county boundary. Here the Indian River ends abruptly
as an open water lagoon and becomes a valley with its floor attaining
elevations of some 5 to 10 feet. The younger Mosquito Lagoon inter-
venes between this valley and the active barrier chain to the east. With
the exception of Turnbull Bay, (the estuary of Spruce Creek near New
Smyrna Beach) the floor of this valley generally remains emergent
toward the north until the valley (a relict lagoon) and the present
lagoon merge about 5 miles north of Flagler Beach in Flagler County.
The emerged floor of this relict lagoon becomes an important part of
the urban area of Daytona Beach 30 miles north of the north end of
Indian River. A narrow relict barrier lies between this valley and the
younger Mosquito Lagoon to seaward. The present lagoon also tends to
become increasingly derelict toward the north until the Intra-Coastal
Waterway finally has to resort to 10 miles of canal in the northeastern
part of St. Johns County for lack of a natural connection between
North River at the south and Pablo Creek at the north.
Superficially this increasing dereliction of lagoons to the north
might suggest longshore tilting with uplift at the north. However this
would seem a small possibility, since these former shorelines and
lagoons converge toward the north and differential uplift increasing in
that direction would be expected to produce a coastal prominence
rather than a reentrant.
The Atlantic Coastal Ridge seems to be almost wholly a product
of Pamlico (?) time when sea level was about 30 feet higher than it now
is. Except for its southern extremity in the southern part of the Distal
Zone of the Peninsula, it seems to have been the mainland shore of the
Pamlico sea (see section of this report entitled "The Eastern Valley").
The eastern slope of the Atlantic Coastal Ridge closely resembles
the present submarine slope that is so uniform off-shore from oceanic
beaches throughout the length of the Atlantic Coastal Plain. Such
off-shore submarine slopes drop off seaward, steeply at first, and ever
more gently with distance seaward, until they become sensibly flat at a
depth of about 30 feet and a distance of some half mile to mile
off-shore from the beach. In the case of the relict, Pamlico, off-shore
profile that forms the eastern slope of the Atlantic Coastal Ridge the
higher (landward) end of the profile is about 30 feet above present sea
level. And in many places (as on the Edgewater and Ariel 7V2 minute
topographic maps) the straightness and spacing of contours on the
subaerial Pamlico relict off-shore slope are practically identical with
those of the depth curves on the present submarine slope off-shore
from the present oceanic beach.




GEOLOGICAL BULLETIN NO. 51


It is unusual for such an off-shore profile to pass through a
changing sea level and emerge nearly intact. Ordinarily it would be
masked by the topographic features made by a succession of younger
shorelines which occupied its face during the progression of emergence.
Quite commonly it would be buried beneath lagoonal sediment or a
succession of beach ridges, but the Pamlico off-shore profile seems
generally to have emerged rapidly without being masked by such later
changes. In part this clean, undamaging emergence may result from the
fact that regression of the sea from the Pamlico level seems to have been
caused by a rapid onset of glaciation. It may also have been helped by
the fact that along most of the Florida east coast it was an erosional
shoreline rather than a prograding one. This can be seen in its discor-
dance with earlier shore lines adjacent to landward. Most of these,
expressed in relict beach ridges (Fig. 34), are truncated at angles by the
shoreline erosion that cut the Pamlico relict off-shore scarp.
The Indian River ends abruptly at the north about a half mile
north of the Volusia-Brevard county line. Directly east of this point is
the southern end of a relict barrier or long spit that seems to have grown
southward cutting off the Pamlico shore from the surf of the open sea.
It lies on the landward side of the present Mosquito Lagoon. Perhaps
this is the reason for the precipitate ending of the Indian River. Farther
north lagoonal sediment accumulated at the toe of the Pamlico Scarp in
the lee of this barrier. The southward drift of sand that built this barrier
seems to have been deflected seaward by a contemporaneous phase of
the coastal prominence that now forms False Cape and Cape Kennedy.
This is suggested by a slight seaward turn of the southern, distal end of
this old occluding barrier. This seaward shunting of the long-shore drift
prevented farther southward extension of the barrier, and south of its
distal end the Pamlico shore remained open to oceanic surf until the
off-shore slope emerged in full thirty-foot stature. When sea level rose
again during later, lesser transgressions including the Flandrian it found
the southern part of this relict, Pamlico, off-shore profile low enough
to inundate. Farther north, in the lee of the relict barrier, sediment had
raised the floor of the old lagoon too high to be reinundated by present
sea level and it remains a dry valley.
Such occultation of the Pamlico off-shore slope in Pamlico time
seems responsible for its better preservation in the lee of the relict
barrier-spit north of the north end of the Indian River.
This part of the Atlantic Coastal Ridge is notably free of carbon-
ates, and considering that it still exists essentially in the full stature it
acquired when it was made in Pamlico time, it seems never to have had
much carbonate content. The relict beach ridges of the Eastern Valley,




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