Citation
Pleistocene shore lines in Florida and Georgia

Material Information

Title:
Pleistocene shore lines in Florida and Georgia a report and accompanying map prepared in connection with investigatioons of the land pebble phosphate deposits of southern Florida
Series Title:
Shorter contributions to general geology
Creator:
MacNeil, F. Stearns ( Francis Stearns ), 1909-
Florida Geological Survey
Place of Publication:
Washington
Publisher:
U.S. Govt. Print. Off.
Publication Date:
Language:
English
Physical Description:
95-106 p. : ill., maps, plates ; 29 cm.

Subjects

Subjects / Keywords:
Shorelines -- Florida ( lcsh )
Shorelines -- Georgia ( lcsh )
Geology, Stratigraphic -- Pleistocene ( lcsh )
City of Lake Wales ( local )
Marion County ( local )
Terraces ( jstor )
Scarps ( jstor )
Coasts ( jstor )
Genre:
federal government publication ( marcgt )
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references and index.
Additional Physical Form:
Electronic version available on the World Wide Web as part of the Linking Florida's Natural Heritage Collection.
General Note:
Part of illus. matter folded in pocket.
Statement of Responsibility:
by F. Stearns MacNeil.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
AAA0757 ( LTQF )
AAB3450 ( NOTIS )
000011037 ( AlephBibNum )
03226478 ( OCLC )

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Pleistocene Shore Lines


in Florida and


Georgia
By F. STEARNS MAcNEIL


SHORTER CONTRIBUTIONS TO


GENERAL


GEOLOGY,


GEOLOGICAL


SURVEY


PROFESSIONAL


A report and accompanying map prepared in


connection with investigations
phosphate deposits of southern


of the land pebble
Florida


UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950


1949


PAPER


221-F

























UNITED STATES DEPARTMENT OF THE INTERIOR

Oscar L. Chapman, Secretary

GEOLOGICAL SURVEY

W. E. Wrather, Director


For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington 25, D. C. - Price $1.00 (paper cover)































CONTENTS


Abstract---------- -----
Introduction ---------------------------------
Purpose of investigation _-----------
Acknowledgment - --------
Previous work----------------------------
Methods of present study-------------- -
Fluvial deposits older than the marine terraces - --
The high terrace ---------------------------
The marine shore lines -------
General features--------------------------


Page
95
95
95
95
95
97
98
98
99
99


The marine shore lines-Continued
Okefenokee shore line
Wicomico shore line -----------------------
Pamlico shore line _
Silver Bluff shore line-
Recent coast line -------------------------
Evidence of coastal stability during the Pleistocene
Pleistocene shore lines and phosphate deposits -----
References cited -------------------------------
Index --------------------- ---------------


ILLUSTRATIONS


PLATE 19. Map showing high terrace and Pleistocene shore lines of Georgia and Florida ---------------------------- In pocket
20. Topographic map of part of Citronelle quadrangle showing remnants of high terrace --------------------- Fol. index
21. Part of Fernandina quadrangle showing Silver Bluff lagoon and bar (broad savannah and inner ridge) and Recent
lagoon and bar (now filled in) ------------------------------------------------------------ Fol. index
22. Part of Brooklet quadrangle showing upper part of Okefenokee terrace and Okefenokee shore line along dis-
sected Miocene terrain ------------------------------------------------------------------------- Fol. index
23. Part of Folkston quadrangle showing an Okefenokee lagoon (Durdin Prairie) and bar (Trail Ridge), probably
submerged in this area, and a Wicomico lagoon and bar to the east----------------------------------- Fol. index
24. Aerial photograph showing wave-washed bars on Okefenokee terrace, Polk County, Fla------------------- Fol. index
25. Part of Hinesville quadrangle showing upper part of Pamlico terrace, Pamlico shore-line scarp, and lower part of
Wicomico terrace _-----------Fol. --- ---------------------------------------------------------Fol. index
III


885473-50


Page

101
102
103
104
104
105
1Q5
106
107

















PLEISTOCENE SHORE LINES IN FLORIDA AND GEORGIA


By F. STEARNS MACNEIL


ABSTRACT
Each of the shore lines recognized is marked by a variety of
features, including cliffs, lagoons, bars, and bays. Shore lines
adjacent to previously dissected terrain show cliffs that char-
acterize shore lines of submergence, whereas shore lines adjacent
to preexisting terraces exhibit elongate lagoons and bars that
generally are taken to indicate early to youthful stages of shore
lines of emergence. It is postulated that the subsidence of an
undissected terrace simulates the nearly plane shore profile of
an emerged shallow ocean floor and, inasmuch as the nearly
plane shore profile is the only prerequisite for the development
of the features characterizing shore lines of emergence, that
identical features would result in both cases. All the shore lines
recognized, therefore, represent maximum rises of sea level,
which are ascribed to glacial oscillation.
Four marine terraces and shore lines are recognized between
present sea level and an altitude of 150 feet. The two highest,
the Okefenokee and Wicomico, are correlated with the Yarmouth
and Sangamon interglacial stages, respectively. The next lower,
the Pamlico, is correlated with a mid-Wisconsin ice recession.
The lowest, the Silver Bluff, is regarded as post-Wisconsin. The
widespread fluvial deposits of the Citronelle formation and
terraces above 150 feet, whether fluvial or marine, are referred
to the early Pleistocene or Pliocene.
No basis for the correlation of shore lines with glacial events
is known in Florida and Georgia. The correlation here accepted
is based on the discovery by Leverett that a gravel train de-
rived from Illinoian till passes into Wicomico terrace sediments
along the Susquehanna River.
This study, undertaken to show any possible relationship
between the Pleistocene terraces and the land pebble phosphate
deposits of Florida, indicates that no such relationship exists.
An early Pleistocene age for the phosphate beds is possible, but
the evidence of fossil land mammals indicating Pliocene age is
considered stronger.

INTRODUCTION
PURPOSE OF INVESTIGATION
This paper and the accompanying map were prepared
in connection with investigations of the land pebble
phosphate deposits of southern Florida. In order to
-discover any possible relationship between the phos-
phate beds and the Pleistocene terraces, it seemed neces-
sary to determine what terraces and shore lines exist
and to map the shore lines in the phosphate area more
accurately than has been done in the past. Inasmuch
as some of the Pleistocene shore lines are preserved
only locally, and because the evidence for some of them


lies far afield, the Coastal Plain of Georgia and western
Florida was studied in addition to the peninsula of
Florida.
The map may prove to be a valuable guide in pros-
pecting for heavy mineral deposits in both Florida and
Georgia. The coast of the Pamlico sea in particular is
known to carry large amounts of heavy minerals in
Florida, and possibly deposits of equal value may be
found in Georgia. Likewise, the coastal bars of the
Okefenokee sea (Trail Ridge) have been prospected re-
cently and found to contain concentrations of heavy
minerals. The outer shores of the coastal bars of all
sea-level stages are regarded as more favorable locations
for heavy-mineral prospecting than the inner lagoonal
shores. Deposits now being worked and areas blocked
out for future mining lie along the shore lines of coastal
bars.

ACKNOWLEDGMENT
The writer wishes to express his sincerest thanks to
Dr. Richard F. Flint, of Yale University, for a long
series of correspondence dating from the time the writer
first started work on the coastal terraces. Dr. Flint
offered many ideas and much helpful criticism.

PREVIOUS WORK
An excellent account of the study of Pleistocene sedi-
ments along the Atlantic Coastal Plain up to 1940 has
been given by Flint (1940). Reviewing early work by
McGee, Darton, Shattuck, Salisbury and Knapp, Went-
worth, Campbell, and Cooke, Flint pointed out that
three hypotheses had emerged from these studies: one
favoring a marine origin, another favoring a fluvial
origin, and a third favoring a combination of fluvial
and marine origins. He stated, in summary, that "the
hypothesis of dominantly fluvial deposition in New
Jersey" had been "unchallenged"; that "serious objec-
tions to a hypothesis of chiefly marine deposition in
Maryland" existed, that there was "evidence of both
marine and fluvial deposition in Virginia," and finally
that "widespread evidence (chiefly morphologic) of
marine deposition" had been reported from Georgia,
South Carolina, and Florida.







SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


Flint cast doubt on the marine origin of certain higher
features, while supporting the marine hypothesis for
at least the lower scarps and terraces along the Atlantic
seaboard from southern Virginia to Florida, and chal-
lenged C. W. Cooke, an important contributor on the
subject of marine terraces, to show evidence for all the
seven terraces he recognized. Flint stated that in his
opinion only two marine scarps had been proved to exist
in the central Atlantic region, but that there was a pos-
sible third and higher scarp in Georgia and Florida.
Cooke (1941) replied that Flint's requirement of high
seaward-facing scarps for the recognition of marine
shores was entirely too rigorous, for there was no such
feature (other than dunes) along the present seashore
of the Coastal Plain.
In his latest published discussion of the Pleistocene
terraces, Cooke (1945, p. 248) recognizes seven shore
lines and the possibility of an eighth. He regards the
highest shore line, where more than one is referred to a
single interglacial stage, as the culmination of the inter-
glacial stage; the lower shore lines he considers to be
pauses during the ensuing emergence of land. The
names of these shore lines, with their altitudes, age, and
correlation, are as follows:
Altitude
Shore line (feet) Age
Brandywine -- -- 270 Aftonian interglacial stage.
Coharie - --rland -- 2150 Yarmouth interglacial stage.
Sunderland ------------- 1701
Wicomico -------------- 100
Penholoway ------------ 70 Sangamon interglacial stage.
Talbot ----------------- 42
Pamlico -------25 "Mid-Wisconsin recession."
Silver Bluff(?)----- 5
Cooke believes that sea level was progressively low-
ered throughout Pleistocene time, possibly due to the
sinking of some large, unstable part of the earth in, for
example, the North Atlantic Ocean or a part of the
Pacific Ocean. The same amount of water may have
been abstracted from the hydrosphere during successive
glacial stages and restored during the interglacial
stages, but the successive interglacial rises in sea level
were progressively lower along tectonically stable
coasts.
Sufficient topographic or sedimentary evidence is not
available at present to evaluate properly the two highest
shore lines recognized by Cooke. The existence of a
Brandywine shore line appears to be based mainly on
a general widening of present river valleys at about
270 feet, which widening Cooke interprets as marking
the heads of former estuaries; however, the line formed
by the "heads" of these "estuaries" coincides with the
boundary between the Coastal Plain and the crystalline
rocks in Georgia, so that other explanations for the
widening of the river valleys are possible. A slight


break in the slope of the high terrace at about 220 feet
is indicated on topographic maps in western Florida,
but the surface where this break occurs is a narrow rem-
nant and the feature cannot be traced for any distance.
Cooke's 170-foot shore line is not definitely the Oke-
fenokee shore line of this paper. (See p. 101.) His
100-, 25-, and 5-foot shore lines, however, are well
founded and correspond with the altitudes of 100 feet,
25 to 35 feet, and 8 to 10 feet given for three of the shore
lines here recognized. The shore line at 70 feet is well
preserved locally, but the one at 42 feet is obscure. Both
the 70- and 42-foot shore lines were regarded by Cooke
as formed during pauses in the retreat of the sea from
the 100-foot level in late Sangamon time.
Cooke's terrace chronology, in which the highest
\ shore line is the oldest and the lowest shore line is the
youngest, is followed in this paper. His interpretation
seems inescapable in view of the softness of the sedi-
ments that compose the former shore features and the
probability that any subsequent marine transgression
to the same altitude would almost certainly have effaced
them. The only alternative to assigning the shore lines
to different interglacial stages is to assume that they
represent successive stages in a single regression, which
seems unlikely. Cooke's correlation of the Wicomico
terrace with the Sangamon interglacial stage is taken
from Leverett (1934, pp. 32-34), who has shown that
a gravel train along the Susquehanna River is derived
from Illinoian till and passes into Wicomico terrace
sediments.
Flint declined to refer to terraces in his discussion,
inasmuch as any sea floor is irregular and a wide range
of altitudes might be concurrent. He based his shore
lines on remnants of seaward-facing scarps and mapped
such remnants as he could find from the James River
in Virginia to southern South Carolina. He recog-
nized two such scarps: the Suffolk scarp, having a toe
at an altitude of 20 to 30 feet, and the Surry scarp, with
a toe at 90 to 100 feet. He stated that he could recog-
nize no marine features higher than the Suffolk scarp
in this area. In Georgia, however, Flint recognized
V Trail Ridge as a marine feature, rising from a maxi-
mum altitude of 180 feet in the southern part of that
State to a maximum of 240 feet in north-central Flor-
ida. Moreover, Flint told the writer in June 1945 that
he thought marine features were present between alti-
tudes of 200 and 250 feet in western Florida. These
features, he believed, might correlate with the southern
part of Trail Ridge. The terrace remnants in western
Florida are part of the high terrace as here mapped.
The relationship of the Surry scarp to the high south-
ern end of Trail Ridge was considered by Flint (1940,
p. 777) to be obscure. Later, however, he pointed out







PLEISTOCENE SHORE LINES IN FLORIDA AND GEORGIA


that, whereas the Suffolk and Surry scarps maintain
horizontality, the discrepant elevations along Trail
J Ridge suggest tilting to the north (Flint, 1947, p. 440).
This would indicate that coastal stability has existed
since the formation of the Surry scarp, but that coast-
wise tilting probably followed the epoch of the sea that
formed Trail Ridge. Flint did not recognize a definite
shore line above 90 (or 100) feet, but interpreted Trail
Ridge as merely a bar, probably of marine origin and
probably tilted.
Flint's shore lines are summarized as follows:


Shore line
Trail Ridge (?)_
Surry __--_-
Suffolk -_-- -


Altitude
(feet)
S140-240
90-100
20- 30


Age

Yarmouth interglacial stage.
Sangamon interglacial stage.


Flint emphasized the fact that the assigned correla-
tions were pure speculation. Earlier (1942, p. 237) he
had referred the Suffolk scarp to the "Peorian intergla-
cial sub-age" and the Surry scarp .tentatively to the
Sangamon interglacial age.
Substitution of the names Suffolk and Surry for
Pamlico and Wicomico was made, apparently, because
of the feeling that terraces and scarps should have a
different nomenclature.
The latest interpretation of the coastal terraces of
Georgia appears on a geologic map by MacNeil (1947).
The terraces are divided into "older terraced surfaces"
of fluvial or marine origin and "younger terraced sur-
faces" of marine origin. The older terraced surfaces
are referred to in this paper as the high terrace; it com-
-prises some large terraced areas but nevertheless is
greatly dissected in comparison with the lower marine
terraces. The high terrace differs from the lower ter-
races, also, in that it is not bounded on the landward
side by a scarp. The lower terraces are all terminated
-onthe landward side by a seaward-facing scarp, pre-
sumably an abandoned sea cliff. Not only is no sea-
ward-facing scarp found at the innermost edge of the
high terrace, but in most places its inner edge stands
higher than the adjacent landward terrain. This
proves, not that the high terrace is of nonmarine origin,
but merely that it is unquestionably the oldest of the
terraces and that its shore line, if one ever existed, has
been completely destroyed.
Workers who have studied the coastal terraces of the
western Gulf region have been more universally in favor
of a nonmarine origin for the terraces in that area. In
1930 Barton explained the coastal prairies of Texas as a
deltaic plain formed by the coalescing fans of the Pleis-
tocene master streams. Doering (1935) later recog-
nized three "surface formations," the Willis, Lissie, and
Beaumont, which he attributed to fluvial aggradation
during three periods of rejuvenation. Doering believed


the Willis to be the oldest and showed how the materials
of the Lissie and Beaumont formations reached their
present position by being transported through gaps in
the Willis. Fisk (1940, p. 175) subsequently described
the coastal prairies of Louisiana as the work of streams.
After the publication of Flint's paper (1940) on the
Atlantic Coastal Plain, a paper by Price (1947) ap-
peared, supplementing earlier work by Barton and oth
ers and showing that the coastal prairies of Texas were
formed by subaerial deposition. Price stated that
"supposedly emerged coastal Quaternary surfaces were
[believed in early studies to be] composed of different
elements termed terraces and these were expected to
have seaward-facing erosional scarps at their inner mar-
gins." He thus implied the nonexistence of the aban-
doned sea cliffs that led early geologists to regard the
coastal terraces as marine in origin.
Considerable difference of opinion therefore exists
among geologists as to whether the Atlantic and Gulf
terraces are of marine or subaerial origin. Moreover,
there is disagreement among the principal exponents of
marine origin as to how many sea levels there were and
how many resultant scarps and terraces are present.
Those who explain the coastal terraces as being of non-
marine origin regard them as the work of aggrading
streams during periods of glaciation, whereas those who
believe they are marine features attribute them to high
sea levels during interglacial stages. It would seem
possible that the features that are obvious in any area
might depend largely on which set of features predom-
inates and on how destructive each stage was of the fea-
tures of the preceding stage.

METHODS OF PRESENT STUDY
The accompanying shore-line map (pl. 19) is based
chiefly on a study of topographic maps and is intended
primarily to show to what extent the available maps
contribute data to the problem of Pleistocene sea levels.
The shore-line scarps can be recognized easily where
good topographic maps on a 10-foot contour interval
are available, but the scarps are not well shown in areas
mapped on a 20-foot interval and their exact position
can be only estimated. Points at which scarps have
been checked in the field are widely scattered and
comparatively few, considering the size of the area.
Contours shown on the topographic maps of the United
States Engineers, at scales of 1: 250,000 and 1: 500,000,
are only approximately located and indicate merely the
general position of the former shore lines.
The high terrace on the accompanying map is taken,
with some modification, partly from the writer's pre-
vious work on the Tertiary and Quaternary formations
of Georgia (MacNeil, 1947) and partly from the topo-






SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


graphic maps of western Florida. The 150-foot shore
line in parts of Polk and Highlands Counties, Fla., was
taken from aerial photos and over most of the area is
without vertical control.
The map shows terraced surfaces above 150 feet. At
150 feet and lower it shows parts of contours that best
locate the features of the several sea levels: shore lines,
bars, intracoastal water, and the like. The contours
used are those at 10, 30, 80, 90, 100, and 150 feet. The
two highest recognizable shore lines are close to the 100-
and 150-foot contours. The two lowest shore lines are
placed at 8 feet and 25 to 35 feet, for which the closest
available contours are 10 and 30 feet, respectively. The
30-foot contour was estimated on maps having a 20-foot
contour interval. Submarine bars of the 100-foot level,
some of which assumed the position of coastal bars dur-
ing the ensuing land emergence, are well shown by the
80- and 90-foot contours. The 90-foot contour was used
only on the maps with a 10-foot contour interval.
Former shore lines are not shown exactly by contours.
In areas where scarps are little dissected, the contours
closely approximate the shore lines, but in areas where
the scarps are dissected the former shore lines are in-
dicated mainly by a general concordance of points. The
map here presented thus gives a good impression of the
preservation of the former shore lines.
For most parts of Florida contours were transferred
from quadrangle sheets by template, but those for cer-
tain quadrangles lacking a land net were reproduced
by photographic reduction. All the Georgia quad-
rangles are slightly generalized photographic reduc-
tions. Small-scale maps prepared by the United States
Engineers either were traced directly or were photo-
graphically reduced.

FLUVIAL DEPOSITS OLDER THAN THE MARINE
TERRACES
A blanket fluvial deposit of highly cross-bedded
sands, clays, and gravels exists in Mississippi, Alabama,
and western Florida. This fluvial deposit was named
the Citronelle formation by Matson (1916, p. 168).
The Citronelle formation extends from present sea level
to altitudes of over 400 feet in Alabama and over 500
feet in Mississippi. It has a thickness of about 150
feet in western Alabama. It lies beneath the Pleisto-
cene terraces at a low altitude, but a terraced surface
on the fluvial deposits rises higher than the highest esti-
mated Pleistocene sea levels. It is necessary, therefore,
that a distinction be made both between the fluvial de-
posits of the Citronelle formation and the Pleistocene
marine deposits and between the high terraced surface,
which may be the constructed surface of the Citronelle
formation, and the Pleistocene marine terraces.


The Citronelle formation was referred to the Pliocene
by Matson on the evidence of plants, studied by Berry
(1916), which were supposed to have come from the
formation. More recently, Roy (1939) has showed that
the plants came from a clay that lies unconformably be-
low the Citronelle formation and cannot, therefore, be
used to date the formation. Still more recently, Fisk
(1945) has correlated the Citronelle with one of the
glacial stages, stating that it "falls within the terrain
of the two highest terraces" of the Mississippi River.
No direct evidence has been presented for determining
the exact age of the Citronelle. If it is younger than
the clay containing Pliocene (?) leaves, it can be shown,
also, to be older than the middle and late Pleistocene
marine terraces, so that an early Pleistocene age is pos-
sible. A Pliocene age cannot definitely be ruled out,
however.
The distribution and character of the Citronelle sedi-
ments suggest that they are coalescent deposits of sev-
eral early rivers that emptied into the Gulf of Mexico.
Where the fluvial deposits merge with marine deposits
has not been demonstrated, but it may be below present
sea level.
THE HIGH TERRACE
The high terrace is the dissected surface lying en-
tirely above an altitude of 150 feet. Many remnants of
a terraced surface, believed to have been continuous at
one time, are found in Georgia, western Florida, Ala-
bama, and Mississippi. The surface rises to an alti-
tude of about 250 feet in Georgia, to about 280 feet in
western Florida, and to over 340 feet at Citronelle, Ala.
(pl. 20), where it forms the upper surface of the Citro-
nelle formation. Parts of this terrace, therefore, are
higher than the highest shore line, at an elevation of 270
feet, recognized by Cooke.
The identification of marine terraces in this paper
is based on the coexistence of shore-line scarps, which
are presumably wave-cut cliffs. All terraces up to an
altitude of 150 feet are bounded on the landward side
by seaward-facing scarps, but there is no scarp at the
upper edge of the high terrace. Cooke (1941, p. 457)
points out that the absence of a scarp does not preclude
the existence of a shore line, inasmuch as few scarps
are found along the Atlantic and Gulf coasts today.
Without the evidence of a scarp, however, and until
study of the soils and sediments yields some definite evi-
dence, there seems to be little way of determining what
part, if any, of the terraced surface above 150 feet is
marine and what part is fluvial.
In western Florida the high terrace is greatly dis-
sected, and its remnants terminate on the gulfward side
at an altitude of about 200 feet. The seaward edge
thus lies about 50 feet above the Okefenokee shore line.








PLEISTOCENE SHORE LINES IN FLORIDA AND GEORGIA


Along the Atlantic side, in eastern Georgia, the high
terrace is less dissected. Its seaward edge rises from
an altitude of 150 feet in the south, where it passes be-
neath the Okefenokee terrace, to approximately 180 feet
near Claxton, in the Claxton quadrangle (7),' where its
seaward edge is again about 30 feet above the Okefe-
nokee shore line. North of Claxton the high terrace
has been destroyed.
Any interpretation of the structure of the high ter-
race would be unreliable until more of it has been
mapped topographically. It appears to rise both to the
west and to the north from southeastern Georgia.
On purely speculative grounds, if the Citronelle for-
mation is the result of fluvial aggradation by rivers
during the Pliocene or during the melting of the first
ice cap, the high terrace-or a part of it-is the con-
structed top of the formation. With the rise of sea
level during the Aftonian interglacial stage, the Citro-
nelle formation was partly inundated and a part of its
surface became a subaqueous platform. If the hypoth-
esis of the progressive lowering of sea level during the
Pleistocene is correct, the boundary between the sub-
aqueous terrace and the fluvial terrace might be sought
at a high altitude, but the figure of 270 feet given by
Cooke is regarded as far from proved. During the
Kansan stage of glaciation rivers cut gaps in the high
terrace. In the ensuing Yarmouth interglacial stage
sea level rose to an altitude of 150 feet, and at that level
river-borne materials reached the sea through gaps in
the high terrace and were distributed coastwise by
oceanic waves and longshore currents.
The high terrace, therefore, is believed to be of sub-
aerial origin. Subsequent to its formation a part of it
may have been inundated by the sea and possibly modi-
fied, but no conclusive evidence to indicate that the sea
ever transgressed it to an altitude higher than 150 feet
has been put forth. The terraces below 150 feet are
believed to be entirely of marine origin.

THE MARINE SHORE LINES
GENERAL FEATURES
The shore lines here recognized are as follows:
Shore line Altitude Age
(feet)
Okefenokee ---- - 150 Yarmouth interglacial stage.
Wicomico ------------- 100 Sangamon interglacial stage.
Pamlico --------25-35 Mid-Wisconsin glacial reces-
sion.
Silver Bluff-------- 8-10 Post-Wisconsin.
All these shore lines are regarded as peaks of marine
transgression. Minor shore lines believed to have been
formed during pauses in the following regression, such

1 Numbers in parentheses are quadrangle numbers on index map of
plate 19.
885473-50- 2


as Cooke's Penholoway and Talbot shore lines, either
have not been dealt with or are referred to as "late
stages."
The shore lines of this report are characterized from
place to place both by open, steeply cliffed mainland
and by more complex coasts combining embayments,
lagoons, and offshore bars. Where offshore bars are
developed, there are really two shore lines, an inner
shore line facing the lagoon and an outer shore line
facing the open sea.
The coastal shore is here defined as the shore facing
the open sea-the shore of the mainland, where it is
unobscured, and the outer shores of offshore bars where
they are developed. The coastal shore line is the out-
line of the coastal shore; the intracoastal shore is the
shore of lagoons or bays partly enclosed by bay-mouth
or offshore bars; and the intracoastal shore line is the
outline of the intracoastal shore.
The precise altitude of the high-tide mark along an
abandoned shore probably cannot be determined with-
out a study of all the coastal features. The shore line
has been variously located at the toe of the scarps and
on or above the scarps. This is apparently due to the
fact that the scarps have been interpreted as sea cliffs
by some geologists, as steep beaches by others, and as
scour zones at the line of breakers by still others.
Probably scarps representing all conditions exist within
any one set of coastal features, so that the problem is
to determine which part of the coast will indicate the
true sea level most accurately. Probably the toe of the
scarp off a coastal bar is the least likely indicator, be-
cause this scarp is being carved by the undertow of
breakers and is well below water level. The bars them-
selves may be submerged. A steep, unindented coast is
unreliable, so far as indicating the high-water mark is
concerned, because the water off such coasts is naturally
deeper at some places than others and also because
erosion of such a coast might produce an even profile
from the top of the cliff to the scour zone at the line
of breakers. The nips cut along the landward side of
shallow lagoons by comparatively small waves should
most nearly approximate the high-water mark. Even
these may be a few feet too high, however, owing to the
fact that the base of lagoonal and estuarine bluffs
usually is cut by storm waves.
The Silver Bluff shore line is sharply defined, but the
10-foot contour, the only contour that is available to
show its features, is probably the upper limit of possi-
bility for its high-water stage. An altitude of 8-feet
for the Silver Bluff sea level is probably correct within
2 feet. The Pamlico shore line also is well preserved.
The toe of the scarp along certain intracoastal shores is
close to 40 feet, but the high-water mark was probably a
little lower than the toe. The 30-foot contour was








SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


selected to show the coastal features of the Pamlico
coast and is probably correct within 7 or 8 feet for the
Pamlico sea level. An altitude higher than 30 feet is
more likely than a lower altitude. Both the Wicomico
and Okefenokee shore lines are approximate, and the
100- and 150-foot contours used to outline their features
are probably correct within 10 feet for the altitude of
their shore lines.
Spits and capes are frequently found along the aban-
doned coasts opposite features similar in size and shape
on the Recent coast. The concordance of the bars and
spits of the Pamlico coast with similar features along
the present-day coast may be noted-for example, the
alinement of a point near Medart in the Arran quad-
rangle (90) in western Florida with the Recent Light-
house Point in Franklin County and the similarity of
bars developed around the north end of Lake Butler
in Pinellas County and the Recent Anclote Keys. This
concordance illustrates to what extent these features
were dependent then as now on bedrock formations and
a source of sand. Both the old and the new features
approximate the edge along which the sandy Miocene
formations crop out, whereas the coast line between
them is underlain by older limestones on the eroded
Ocala uplift. The limestones furnish no sand, and the
shore is mainly muddy.
Another feature on the Pamlico coast is the small
festoon of islands shown in the Tates Hell Swamp quad-
rangle (111) in Franklin County, Fla. These islands
may be evidence that a large river, probably the Apa-
lachicola, emptied in this area in Pamlico time. They
compare favorably with the islands now found at the
mouth of the Suwannee River.
Some peculiarities of the Recent coast are due to the
coexistence of Silver Bluff and Recent lagoons, which
may have resulted both from the depth of the Silver
Bluff lagoons and from the comparatively slight drop
in sea level since Silver Bluff time. This is especially
well shown by the Indian River, a Silver Bluff lagoon
that is still inundated, and by Mosquito Lagoon and
the Banana River, Recent lagoons, in Brevard County,
Fla.
Where Silver Bluff lagoons have been filled in, Silver
Bluff and Recent coastal bars have a double structure.
This is illustrated by the Sea Islands. Amelia Island
(pl. 21) in northeastern Florida and Cumberland
Island in southeastern Georgia both have an inner
ridge, built as a dune-covered bar during Silver Bluff
time, and a high outer dune-covered bar built by the
Recent sea. The two dune areas are separated by a
swamp, formerly a narrow lagoon.
The terrace deposits below altitudes of 150 feet in
peninsular Florida and in Georgia in no way resemble


the highly cross-bedded sands, clays, and gravels of the
Citronelle formation. There is no apparent difference
in the appearance of the sand on the various lower ter-
races. The materials are well sorted and consist of
fine- to medium-sized sand grains. Histogram studies
of a few samples from central peninsular Florida, car-
ried out by J. B. Cathcart, Jr., in connection with
phosphate studies, indicate that they most nearly
resemble beach sands.
The general land gradient has much to do with the
preservation of both scarps and terraces, as can be seen
by a comparison of the Okefenokee shore line and ter-
race in the Brooklet quadrangle (4) in Bulloch County,
Ga., an area of low gradient, with the same shore line in
Walton and Okaloosa Counties in western Florida, an
area of steep gradient. A shore-line scarp is always
sharper and steeper where it adjoins an area that was
previously dissected, such as that in the Brooklet
quadrangle (4). It may be practically indistinguish-
able, however, where superimposed on a previously
existing terrace such as the Okefenokee shore line,
where it transgressed the high terrace along the western
edge of the present Okefenokee Swamp, or the Pam-
lico shore line, where it transgressed the Wicomico
terrace in the Owens Bridge (98) and Thousand Yard
Bay (99) quadrangles in western Florida.
Strikingly shown by this map is the high degree of
duplication of compound coastal features on each of the
four abandoned shore lines along the Atlantic Coast,
as well as the location of later and lower features com-
pletely outside the coastal shore line of the next higher
sea level. The coastal features of the Wicomico sea lie
wholly outside the coastal shore line of the 'Okefenokee
sea, the Pamlico coastal features outside the coastal
shore line of the Wicomico sea, the Silver Bluff coastal
features outside the coastal shoreline of the Pamlico sea,
and the Recent lagoons and coastal bars outside the
coastal shore line of the Silver Bluff sea.
The open, steeply cliffed shore line, of which the
Okefenokee shore line in Bulloch County, Ga., is a
well-developed example, is the type that normally, ac-
cording to Johnson (1919) and Lobeck (1939), indi-
cates subsidence; in this instance, it is believed to be due
to inundation caused by a rise of sea level. In south-
ern Georgia and northern Florida, however, the Oke-
fenokee shore line, as well as the lower shore lines, shows
a good development of offshore bars enclosing lagoons
of greater or lesser size. This type of shore line is
taken by both Johnson and Lobeck to indicate the
emergence of land. According to them, when a shallow
ocean floor is elevated above water level so as to produce
a nearly plane shore profile, an offshore bar is immedi-
ately built up by the scouring of the bottom by the


100








PLEISTOCENE SHORE LINES IN FLORIDA AND GEORGIA


undertow along the line of breakers offshore, and the
material dislodged is deposited as a bar in front of the
line of breakers. Although this process was postulated
to follow the emergence of a nearly flat ocean floor, the
only physical requirement for the operation of the
process is the existence of a nearly plane shore profile.
It is here postulated that, where a preexisting undis-
sected terrace is submerged, the same process will occur.
OKEFENOKEE SHORE LINE
The term "Okefenokee" was introduced by Veatch
and Stephenson (1911, pp. 60, 424-434) as a formation
name and was later used by Cooke (1925, p. 35) as the
name of a terrace constructed on deposits of that age.
Cooke defined the terrace as lying between the altitudes
of 100 and 160 feet. Later he abandoned the name in
favor of "Sunderland terrace," fixing the upper limit
at 160 feet. Still later he defined the Sunderland ter-
race as having an upper limit of 170 feet. Cooke
informed the writer in March 1949 that he now believes
there is a "lower Sunderland terrace" with a shore line
at 140 feet. Inasmuch as there is some doubt that the
highest shore line in Georgia here recognized is equiva-
lent to the Sunderland shore line of Maryland, the
name "Okefenokee" is revived for the terrace.
The Okefenokee shore line is well developed in
Bulloch County, Ga., and is well shown by a scarp in
the Brooklet quadrangle (4). The scarp, which appar-
ently was a cliff facing the open sea, is poorly developed
or destroyed to the north of this area. In Bulloch
County the cliff borders a highly dissected Miocene
terrain (pl. 22), but farther south in Tattnall and Long
Counties it borders remnants of the high terrace. The
altitude of the edge of the high terrace drops to the
south, and a slightly projecting cape near Redland in
Wayne County may mark the point at which it passed
below the level of the Okefenokee sea. From here
southward the coastal shore line passed from the main-
land to a narrow elongate bar (Trail Ridge), and the
sea transgressed the high terrace for some distance to
form a shallow intracoastal bay or sound (the present
Okefenokee Swamp). In Brantley and northern Charl-
ton Counties, Trail Ridge was mostly submerged (pl.
23), but in southern Charlton County parts of it ex-
tended 20 to 30 feet above water. The Okefenokee
lagoon had a maximum depth of about 30 feet.
Trail Ridge widens in Bradford and Clay Counties,
Fla., to a large pear-shaped promontory; the southern
end probably is an island of older terrain rather than
a bar. The lagoon west of Trail Ridge apparently
shallowed to the south and was about 20 feet shallower
in southern Baker and northern Bradford Counties
than in southern Georgia.


Three irregular, roughly parallel ridges stood as
islands in the Okefenokee sea in Polk and Highlands
Counties in central peninsular Florida. The one
farthest east is known as the Lake Wales ridge. Ter-
raced surfaces surrounding these ridges terminate
abruptly at 150 feet, and aprons of white sand extend
outward from the actual shore line for a short distance.
These aprons were presumably submarine extensions of
the beaches, the sand having been derived from the ero-
sion of nips in the central highland ridges. Smaller
promontories were reduced by marine abrasion to
wave-washed bars (pl. 24). An irregular thin white
sand dune is occasionally found above 150 feet, but sel-
dom above 225 feet. The terrain above the 150-foot
contour is hilly, with many characteristic round lakes.
Except where these lakes are now being drained and
their altitude has been lowered to a level below 150
feet, no lakes of this type are present below the 150-foot
contour, and presumably any that existed were filled
in by the Okefenokee sea. Inasmuch as the lakes,
which are probably sinkholes, are present in the sandy
hills but have been effaced on the adjoining terrace, the
ridges could hardly be bars formed by the Okefenokee
sea. The central highlands undoubtedly represent a
topography older than the Okefenokee terrace.
High hills between Dade City and Brooksville, in
Pasco and Hernando Counties, also stood as islands
during the Okefenokee transgression. They are be-
lieved to be composed of beds of the Hawthorn forma-
tion (middle Miocene), leached in place. To the north,
in Citrus, Levy, and Marion Counties, numerous small
hills stand above an altitude of 150 feet. Islands
existed here, but their exact shape can hardly be in-
ferred on the basis of topography in an area where Re-
cent sinkholes are so abundant.
Another large area, composed of rocks of the Haw-
thorn formation, formed an island farther north in
Alachua County. This area and the blunt southern
end of Trail Ridge comprised the largest group of is-
lands in the Okefenokee sea in Florida. Other large
islands existed in southern Baker, Columbia, Suwannee,
and Hamilton Counties; with the island in Alachua
County, they mark the irregular upturned edge of the
Hawthorn formation around the east and north sides
of the Ocala uplift. These islands enclosed the in-
tracoastal water of southeastern Georgia on the south.
The intracoastal shore line of the Okefenokee sea en-
tered Florida in northern Hamilton County, but its
location from there to the vicinity of Tallahassee is
indefinite.
A fairly straight shore line with several small, sub-
merged offshore bars extended from Tallahassee to the
Bristol quadrangle (60) on the Apalachicola River.








SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


It is poorly preserved or not mapped topographically
from there to eastern Walton County. From T. 1 N.,
R. 18 W., in Walton County to T. 1 S., R. 25 W., ini
Okaloosa County, however, the Okefenokee shore line
is fairly well defined by a series of concordant points
arranged in a gentle arc, although the general terrain
is highly dissected. No uniformity exists from this
region to the Alabama line.
The Okefenokee shore line does not appear to deviate
appreciably from an altitude of 150 feet anywhere
along its visible extent. It is well preserved in Georgia,
in northern Florida, and along both sides of the Lake
Wales ridge and two smaller ridges that make up the
central highlands of peninsular Florida. Yet altitudes
along the crest of Trail Ridge rise to the south. The
Lake Wales ridge is coaxially alined with Trail Ridge.
The highest point in Florida, the hill on which the
Bok Tower stands, at an altitude of 325 feet, is located
on the Lake Wales ridge. If the Lake Wales ridge is
a continuation of Trail Ridge on the other side of the
Ocala uplift, then altitudes along its crest increase from
about 140 feet in Georgia to 280 feet in northern Florida
and 325 feet in central Florida. If these discrepant
altitudes indicate coastwise tilting, as suggested by
Flint (1947, p. 440), it is of pre-Okefenokee age and
may indicate that the Florida peninsula was raised
slightly in late Pliocene or early Pleistocene time. The
apparent continuity of Trail Ridge with the Lake Wales
ridge is due largely to the fact that they both lie along
the broadly arcuate Okefenokee coast line, some parts
having been constructed and other parts carved to con-
form with it. If the large southern end of Trail Ridge
and the Lake Wales ridge are part of an older terrain,
they might well reflect pre-Okefenokee tilting, but
there is little to indicate tilting of the Okefenokee bar
that forms the northern part of Trail Ridge.
WICOMICO SHORE LINE
The Wicomico shore line is the least sharply defined
of the shore lines recognized, which might indicate that
the sea stood at this level for a comparatively short
time. Fairly well developed marine features are shown
by the 100-, 90-, 80-, and 70-foot contours. In some
areas the 70- and 80-foot contours mark the top of the
Pamlico scarp, so that any lower features formed dur-
ing the withdrawal of the sea from the 100-foot stage
were effaced. Theoretically the sea stood at every
altitude during a withdrawal from its maximum rise
to its lowest fall, and it is possible that some of the
offshore bars associated with this shore line represent
several minor pauses in the withdrawal of the sea from
a maximum rise of 90 to 100 feet. References to the
Wicomico shore line will be made in terms of early ard


late stages, which are comparable to differences between
the Silver Bluff and Recent shores.
The highest shore line Flint could recognize north
of Georgia he named the Surry scarp, and he deter-
mined the altitude of its toe as being between 90 and
100 feet. This is undoubtedly the shore line that had
been known previously as the Wicomico. The scarp
was traced by Flint from the James River to a point in
the north-central part of the Pineland quadrangle (3)
of South Carolina and Georgia. The Pineland quad-
rangle is shown in its proper position on the map, and
the southernmost extension of the Wicomico scarp as
traced by Flint is indicated by an arrow. The Wi-
comico scarp at this point appears to have been an
intracoastal shore line, at least in its late stages, judging
from the way a series of offshore bars appears to di-
verge from it to the north. Between the Savannah
River and the Altamaha River, the Wicomico shore line
is very irregular, but a good alinement of bars offshore
is shown by the 80- and 90-foot contours in the Egypt
(5), Meldrim (9), Pembroke (8), and Hinesville (13)
quadrangles. This indicates that in late Wicomico
time at least a good deal of intracoastal water existed
in this area. There appears to have been a weakly pro-
jecting cape just north of the present Altamaha River
in early Wicomico time, but a sharp cape projected
southeastward into the northern part of the Ludowici
quadrangle (18) in late Wicomico time. South of the
Altamaha River the Wicomico scarp merges with Trail
Ridge and is congruent with the Okefenokee scarp as
far south as western Duval County, Fla. Well-defined
bars were present in late Wicomico time both north and
south of the St. Marys River.
The features of the Wicomico shore line attributed to
late stages, particularly for the part of the coast north
of the Altamaha River in Georgia, strongly recall the
present compound coast of North Carolina. This type
of coast probably resulted from the inundation of pre-
existing drainage systems for a short period-not long
enough for the sea to have completely destroyed coastal
promontories of soft rocks, but long enough for the depo-
sition of flat, terracelike estuarine and adjacent sea
floors. With subsequent withdrawal of water, the newly
formed shallow floors emerged, and coastal bars typical
of shore lines of emergence were constructed.
In Clay, Putnam, and Alachua Counties, Fla., the
Wicomico shore line was very irregular; the sea proba-
bly inundated valleys in a prominent terrain of
weathered Miocene rocks.
The Wicomico shore line follows the east side of a
ridge in Marion, Lake, and Orange Counties that is here
designated the Orlando ridge. One island was located
on this ridge in northern Marion County. From south-


102







PLEISTOCENE' SHORE LINES IN FLORIDA AND GEORGIA


ern Marion County the shore line extended to south-
central Orange County, where it formed a pronounced
cape southeast of Orlando. From this point the shore
line cut back sharply to the west as far as southeastern
Lake County and then turned abruptly southward, fol-
lowing the east side of the Lake Wales ridge to a point
south of Lake Childs. A narrow bar east of Lake
Arbuckle in southeastern Polk County forms the pres-
ent divide between the Kissimmee River and the drain-
age into Lake Istokpoga.
The Orlando ridge, passing below the 100-foot con-
tour in southern Orange County, continues with de-
creasing altitude through eastern Osceola County,
northeastern Okeechobee County, and western St. Lucie
County into western Martin County. During late
Wicomico time a long, narrow peninsula extended as
far as southeastern Osceola County. It is probable
that the low southern end of the Orlando ridge is
younger than the part from Orange County northward
and that it grew southward during the retreat of the
Wicomico sea. The southern limit of all coastal bars
along the eastern coast of Florida probably was and is
being extended by slow movement of sand by south-
ward-moving longshore currents.
The Wicomico shore extended from a point south of
Lake Childs northward to a point northwest of Sebring
and thence irregularly around the uplands of central
Florida. Throughout this area it is expressed as a low
scarp cut in the older Okefenokee terrace. It extended
along the west side of the Orlando ridge from Lake
Apopka to central Marion County, where it rejoined the
eastern shore line. Large islands were present in
Pasco, Hernando, Citrus, Sumter, and Marion Counties.
From the vicinity of Gainesville, the Wicomico shore
line roughly paralleled the strike of the Miocene beds
around the Ocala uplift to Tallahassee.
The Wicomico shore line was irregular in western
Florida. A general concordance of points indicates
that it extended in a gentle arc north of Choctawhatchee
Bay, paralleling the older Okefenokee shore line. In
late Wicomico time some well-defined bars were con-
structed east of the Ochlockonee River in the Smith
Creek (88) and Bradwell Bar (89) quadrangles.
PAMLICO SHORE LINE
The Pamlico is the best preserved of the Pleistocene
shore lines. It represents an advance of the sea to an
altitude of about 25 to 35 feet following the retreat of
the Wicomico sea to an unknown depth.
A series of large bars, similar to the present Sea
Islands, was present all the way across the Coastal Plain
of Georgia. These bars may have impounded a great
deal of intracoastal water during early Pamlico time,


but it is possible that in late Pamlico time this area
was silted in and was largely salt-marsh savannah, sim-
ilar to the Recent savannahs. At least it is certain
that the sharp scarp (pl. 25) extending from south-
eastern Effingham County to western Camden County,
Ga., was an intracoastal shore line and that the coastal
shore line was located along bars well to the east in early
Pamlico time.
The coastal shore line is very well preserved along
the east side of large bars, not far from the present
coast, from the St. Marys River to central Flagler
County, Fla. Narrow coastal bars extended from
southern Brevard County. The long St. Johns River
valley was a large intracoastal bay in which there were
several large islands. No contour maps are available
to show the Pamlico bars south of Brevard County;
possibly the intracoastal water joined the open sea in
this area.
The shore line of the lagoon in southern Brevard
County continued southward through Indian River and
St. Lucie Counties and extended around a sharp cape,
in southwestern Martin County, that marks the low
southernmost end of the Orlando ridge.
From this sharp cape the Pamlico shore line extended
around the north side of Lake Okeechobee; it then
trended southwestward nearly to the Caloosahatchee
River and from that point northwestward toward
Sarasota Bay. It is marked by a low scarp cut in the
Wicomico terrace in this area. A large, low island
existed south of the Caloosahatchee River.
A larger and more open estuary occupied the region
of present Tampa Bay. Several islands existed at the
time, the largest of which are in Pinellas County, one
about on the site of St. Petersburg and two others to
the northwest between Seminole and Tarpon Springs.
A strait apparently existed across the present site of
Lake Butler, and a strong, curved spit extended around
the lake's north end. This spit, the Pamlico counterpart
of the Recent Anclote Keys, is the last sandy feature
along the stretch from southern Pasco County to Light-
house Point in Franklin County.
During Pamlico time, as now, the shore from Pasco
County to Wakulla County was probably muddy or
had comparatively small amounts of sand derived from
older terraces. The bedrock in this area consists of
early Tertiary limestones, exposed by weathering of
the Ocala uplift, and was not a source of sand.
Apalachee Bay in Pamlico time extended as far north
as southern Leon County, but its shore line swung
abruptly southward southwest of Tallahassee along the
scarp of the middle Miocene beds on the west side of
the Ocala uplift. The west side of Apalachee Bay in
Pamlico time thus falls in line with the west side of


103







SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


the Recent bay, and a hooked cape near Medart in the
Arran quadrangle (90) corresponds to a similar feature
in eastern Franklin County. From this cape, the Pam-
lico shore line cut across the older Wicomico terrace
in a more or less westerly direction. A small arcuate
group of islands in the Tates Hell Swamp quadrangle
(111) in Franklin County is comparable to islands off
the mouth of the Suwannee River and suggests that
possibly the Apalachicola River emptied at this locality
in Pamlico time. Several high bars along the north
side of St. George Sound may or may not have been
formed during Pamlico time.
West of the Apalachicola River the Pamlico shore
line extended across the Wicomico terrace to a cape at
Panama City, and from there westward the coastal
shore line can be followed along a series of bars
concordant with the present coast. West Bay and
Choctawhatchee Bay were large embayments. West of
Choctawhatchee Bay the Pamlico bars were along the
north side of the Recent Santa Rosa Sound, and intra-
coastal water was present in the East Bay River inlet
and an enlarged Pensacola Bay. West of Pensacola
Bay was a series of bars and spits.
SILVER BLUFF SHORE LINE
The name "Silver Bluff" is of comparatively recent
usage (Parker and Cooke, 1944). Cooke first used it
definitely for the name of a shore line in 1945 (Cooke,
1945, p. 248). Reports of a very late drop in sea level
of about 6 to 8 feet, however, have come from world-
wide sources. Probably one reason it has not been
mapped before is the lack of accurate small-interval
topographic maps along the coast. Although the 6- or
8-foot contour would more accurately locate the toe of
its scarp, the 10-foot contour brings out its features in
sufficient detail for mapping.
The Silver Bluff intracoastal shore line in Georgia is
very well marked by the inner edge of the coastal
savannahs. The Sea Islands lying outside have a dou-
ble structure consisting of a higher inner ridge and
a lower outer ridge, generally separated by a narrow
swamp (pl. 21). The higher inner ridge represents the
Sea Islands of Silver Bluff time; the coastal shore line
lay along the outer margin of these islands. The strip
from 6 to 8 miles wide between these islands and the
present inner edge of the savannahs was intracoastal
water. The intracoastal zone narrowed in Florida and
followed the present course of the Amelia River, the
South Amelia River, Sisters Creek, Pablo Creek, Cab-
bage Swamp, and the Tolomoto River north of its junc-
tion with the Guano River. Coastal bars of the Silver
Bluff sea are again preserved south of the middle of the
Matanzas quadrangle (142) and are present in the
northern and also in the southern part of the Ormond


quadrangle (145). A few small bars were present near
Port Orange and New Smyrna in the Port Orange
quadrangle (148). Silver Bluff intracoastal lagoons
between the Matanzas quadrangle (142) and New
Smyrna occupied narrow, unnamed depressions.
South of New Smyrna no accurate topographic maps
are available. A part of Merritt Island in Brevard
County rises above an altitude of 10 feet, and appar-
ently the Indian River in this area was a lagoon during
Silver Bluff time. A cape corresponding to the Recent
Cape Canaveral was located on Merritt Island.
The 10-foot contour is shown, also, on topographic
maps in western Florida. In this area the Silver Bluff
coastal shore line was located along the present intra-
coastal shore line in places and along the present coastal
shore line in others. A large bay existed in southern
Gulf and western Franklin Counties, and it appears
that the Apalachicola River shifted its course to empty
into this depression after having silted up its mouth a
little to the east in late Pamlico time. Some well-
defined bars are found east of St. Joseph Bay; they
curve, curiously, in a direction opposite to Recent St.
Joseph Spit. All the present bays in western Florida-
St. Andrews Bay, West Bay, Choctawhatchee Bay, and
Pensacola Bay-were larger in Silver Bluff time.
The Silver Bluff age might be tentatively correlated
with the so-called "climatic optimum" of glacial geol-
ogists, botanists, and zoologists, a period about 6,000 to
4,000 years ago when the climate was appreciably
warmer than now. For many reasons it is regarded as
the peak of the Recent interglacial stage.
RECENT COAST LINE
The closely spaced, often concentric, arrangement of
Silver Bluff and Recent features makes it highly proba-
ble that present sea level is merely a retreat from the
Silver Bluff level. This change, if true, makes an
adequate standard for comparing the early and late
stages of former retreats of sea level.
The coast line on the Atlantic side in Georgia and
Florida is being built up, probably because of the local
occurrence of soft reworkable sediments and the large
volume of fresh sediments carried to the sea by the
Georgia rivers and on southward by longshore currents.
In this region practically every Silver Bluff feature has.
a Recent analog. There is little indication that Recent
features mimic Silver Bluff features on the Gulf side,
however, and around St. Joseph Bay in western Florida
the Recent features depart radically from Silver Bluff
forms. At least along the interval from Anclote Keys
to the western edge of Apalachee Bay the coast appears,
to be undergoing destruction, probably because of solu-
tion of the clastic-free limestones on the Ocala uplift,
and the absence of plastic residues.







PLEISTOCENE' SHORE LINES IN FLORIDA AND GEORGIA


EVIDENCE OF COASTAL STABILITY DURING THE
PLEISTOCENE
Extreme caution has been urged by some physiog-
raphers in the correlation of Pleistocene shore lines
from place to place, and it is argued that shore lines
at the same altitude at widely separated points do not
necessarily indicate the continuity of a shore line at
that altitude. Most of this caution, at least as far as the
Atlantic coastal region is concerned, appears to stem
from a foregone conclusion that the coast has been tilted
recently and that therefore the terraces and shore lines
must be tilted. The basis for this conclusion is proba-
bly the concept, now almost classical, that coastwise
tilting along an axis close to Cape Hatteras has drowned
the coast to the north and elevated the coast to the south.
The study of former shore lines along the Atlantic
coast has advanced to the stage where it is no longer
dependent on observations at scattered points. These
shore lines can be traced for miles on topographic maps
with only local gaps, which obviously are made by
streams. Furthermore, these maps were prepared by
men whose only interest was topography and who were
not especially concerned with the significance of the
features they were mapping. Not only are the nips and
sea cliffs preserved, but it can also be shown that many
other coastal features, such as bars, lagoons, spits, and
capes, are present and that these are all a part of the
abandoned coasts. It is entirely possible that simple
scarps might be miscorrelated from place to place, but
it is unlikely that one related set of coastal features
could be confused with another set that lies wholly
separated from it.
The Pamlico (Suffolk) and Wicomico (Surry) scarps
were found by Flint to maintain their altitudes from
the James River in Virginia to the Savannah River.
The present writer has found that the shore-line scarps
in Georgia and Florida do not appear to deviate from
their altitudes in any significant degree and that any
possible coastal warping involving the middle and late
Pleistocene shore lines must be a matter of inches or
a few feet, never enough to make one shore line in-
distinguishable from another.
It seems to this writer that continental tilting does
not imply that Pleistocene shore lines have been tilted
and that the only bearing the altitude of the shore
lines might have on the continental tilting would be
to date it tentatively. Continental warping or tilting
is certainly indicated by the distribution of the Creta-
ceous to Miocene sediments of the Atlantic Coastal
Plain, which extend to altitudes high above present sea
level in the south but are known to lie below sea level
off the coast of New England. The Pleistocene shore
lines from Maryland southward are not tilted, however,


so that the continental tilting does not appear to be of
Recent date.
Some of the bays that indent the coasts of North
Carolina, Virginia, and Maryland are carved in late
Tertiary sediments and were excavated subsequent to
the deposition of the high-terrace gravels, which are of
Pliocene or early Pleistocene age. It is suggested that
these bays are drainage systems that were excavated
during the Pleistocene glacial stages when the sea stood
far below present sea level. The lack of deep embay-
ments along the south Atlantic coast suggests that the
rivers of the south were aggrading their beds while
the rivers of the north were cutting theirs. The drain-
age systems of the North Carolina, Virginia, and Mary-
land coasts are now inundated simply because of the
rise of sea level due to the melting of glacial ice.
The large embayments of western Florida (Pensa-
cola Bay, Choctawhatchee Bay, St. Andrews Bay, and
others) and of southwestern peninsular Florida (such
as Tampa Bay and Charlotte Harbor) have likewise
been considered evidence of Recent subsidence of the
land. Stumps standing a few feet off shore in western
Florida have been taken to indicate that the land is
being inundated. If, however, the Recent shore line
is a retreat from the Silver Bluff level, another explana-
tion is needed. Stumps could be left standing in water
by the cutting back of a forested shore without land
subsidence and even with land emergence, if the rate
of cutting was greater than the rate of emergence. It
seems more likely that these embayments also are middle
and late Pleistocene drainage systems and that they
were drowned more than once during Pleistocene time,
not as a result of land subsidence, but as a result of
the oscillation of sea level. During Wisconsin glacia-
tion streams flowed through them and they were prob-
ably cut deeper, whereas during Silver Bluff time the
water in them was deeper than now.

PLEISTOCENE SHORE LINES AND PHOSPHATE
DEPOSITS
This investigation was undertaken to determine
whether any part of the land pebble phosphate deposits
of Florida is of Pleistocene age. The main body of the
phosphate deposits, together with subsidiary sand and
clay, constitutes the Bone Valley formation, now known
to extend over southern and western Polk County,
eastern Hillsborough County, and northern Hardee and
Manatee Counties, Fla. Leached areas of the under-
lying Hawthorn formation, here a limestone, also are
mined for phosphate. Owing to erosion, the Bone
Valley formation terminates in a feather edge to the
west and to the north but, according to information
obtained by drilling, passes into less phosphatic beds


105







SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949


to the east and to the south. The Bone Valley forma-
tion has been assigned to the Pliocene on the basis of
land and marine mammals contained in it. It has been
correlated with the Caloosahatchee marl of southern
Florida, and the Caloosahatchee marl contains a large
molluscan fauna that has been the standard for the
Pliocene in the eastern United States for many years.
Vernon (1943, p. 156) states that the phosphate de-
posits are confined beneath terraces, "one with flats
developed near 100 feet above sea level, one with flats
near 150 feet, and possibly a third in the land pebble
field, that are approximately 212 feet above sea
level. * * * These terraces are separated by escarp-
ments and have been described in detail by Cooke, who
believed them to be remnants of former marine plains."
Vernon states further that "the fact that phosphate
occurs in at least two different beds indicates that the
accumulation of Florida phosphate rock was not during
one phase, as believed by most writers, but during at
least two, and probably more."
Although no geologic age is mentioned, this is clearly
an assignment of the Bone Valley formation to the
Pleistocene and an assertion that, instead of being a
single deposit, it consists of separate formations de-
posited during different interglacial periods.
Work on the phosphate deposits by the United States
Geological Survey began in 1948 under the direction of
the writer and continued under J. B. Cathcart, Jr.
Isopach maps and cross sections were prepared from
information supplied by mining companies, current
drilling was observed, and pits were examined, but the
existence of several phosphate-bearing terrace deposits
has not been verified. Instead, the phosphate gravels
appear to be a continuous beach placer deposit resting
disconformably on a very irregular limestone surface.
The underlying limestone also contains phosphate
nodules; where leached, it forms a deposit of high com-
mercial value, rich in flotation-sized particles. No
breaks in the extent or altitude of the phosphate gravels
were detected at either the 100- or the 150-foot contour,
and the phosphate was found to extend under the high
hills above 150 feet as well as under the adjacent
Okefenokee terrace. The phosphate gravels terminate
abruptly at the Pamlico shore line, however, appar-
ently because of destruction by the Pamlico sea, and the
Pamlico terrace deposit contains at its base a thin con-
glomerate of reworked phosphate, washed clean, which
is of no commercial value.
The oldest shore line, at 150 feet, is correlated with
the Yarmouth interglacial stage. It is possible that
deposits of the Aftonian interglacial stage are present
in central peninsular Florida but that they have no


physiographic expression. If so, the phosphate gravel
could be of early Pleistocene age, but all of it must be of
this age. Evidence of fossil mammals indicating a
Pliocene age for the marine deposits is considered
stronger than the mere possibility of early Pleistocene
age. A few alluvial phosphate deposits, no longer of
commercial importance, contain a mixture of Pleisto-
cene and reworked Pliocene fossils and presumably
were reworked by Pleistocene streams.

REFERENCES CITED
BARTON, D. C., 1930, Deltaic coastal plain of southeastern Texas:
Geol. Soc. America Bull., vol. 41, no. 3, pp. 359-382.
BERRY, E. W., 1916, The flora of the Citronelle formation: U. S.
Geol. Survey Prof. Paper 98-M, pp. 193-208.
COOKE, C. W., 1925, Physical geography of Georgia: Georgia
Geol. Survey Bull. 42.
- , 1941, Two shore lines or seven?: Am. Jour. Sci., vol.
239, no. 6, pp. 457-458.
-- , 1945, Geology of Florida: Florida Geol. Survey Bull. 29.
DOERING, JOHN, 1935, Post-Fleming surface formations of coastal
southeast Texas and south Louisiana: Am. Assoc. Petro-
leum Geologists Bull., vol. 19, no. 5, pp. 651-688.
FISK, H. N., 1940, Geology of Avoyelles and Rapides Parishes:
Louisiana Dept. Cons. Geol. Bull. 18.
- , 1945, Pleistocene age of the "Citronelle" [abstract]:
Geol. Soc. America Bull., vol. 56, no. 12, pt. 2, pp. 1158-
1159.
FLINT, R. F., 1940, Pleistocene features of the Atlantic Coastal
Plain: Am. Jour. Sci., vol. 238, no. 11, pp. 757-787.
- , 1942, Atlantic coastal "terraces": Washington Acad. Scl.
Jour., vol. 32, no. 8, pp. 235-237.
- , 1947, Glacial geology and the Pleistocene epoch, New
York, John Wiley & Sons.
JOHNSON, D. W., 1919, Shore processes and shore-line develop-
ment, New York, John Wiley & Sons.
LEVERETT, FRANK, 1934, Glacial deposits outside the Wisconsin
terminal moraine in Pennsylvania: Pennsylvania Geol.
Survey, 4th ser., Bull. G-7.
LOBECK, A. K., 1939, Geomorphology, New York, McGraw-Hill
Book Co.
MACNEIL, F. S., 1947, Geologic map of the Tertiary and Quater-
nary formations of Georgia: U. S. Geol. Survey Oil and
Gas Investigations Preliminary Map 72.
MATSON, G. G., 1916, The Pliocene Citronelle formation of the
Gulf Coastal Plain: U. S. Geol. Survey Prof. Paper 98-L,
pp. 167-192.
PARKER, G. G., and COOKE, C. W., 1944, Late Cenozoic geology of
southern Florida: Florida Geol. Survey Bull. 27.
PRICE, W. A., 1947, Geomorphology of depositional surfaces:
Am. Assoc. Petroleum Geologists Bull., vol. 31, no. 10, pp.
1784-1800.
RoY, C. J., 1939, Type locality of the Citronelle formation, Citro-
nelle, Ala.: Am. Assoc. Petroleum Geologists Bull., vol.
23, no. 10, pp. 1553-1559.
VEATCH, J. 0., and STEPHENSON, L. W., 1911, Geology of the
Coastal Plain of Georgia: Georgia Geol. Survey Bull. 26.
VERNON, R. 0., 1943, Florida Minerals Industry: Florida Geol.
Survey Bull. 24.


106





















INDEX


Page
Abstract --------_ ____________--_--------- 95
Acknowledgment ----------------------- 95

Bone Valley formation---------------------------------- 105-106
Brandywine shore line ------------------------------ - 96

Citronelle formation-------------------------------------- 98, 99.
Coastal shore and shore line--------------------------------- 99
Coharie shore line---------------------------------------- 96
Cooke, C. W., interpretations by--- 96, 98, 99, 101, 104, 106

Duplication of coastal features------------------- 100; pl. 19

Flint, R. F., work by------------------------------ 95-97, 102, 105
Fluvial deposits -----------------------------______------------- 98

Hawthorn formation------------------------------------___ 101, 105
High terrace------------------ ------------------ 98-99 ; pls. 19, 20
High-tide mark, determination of ------------------------- 99


Intracoastal shore and shore line--.
Investigation, present ..... ------
Investigations, previous -- ----


------------ 99
--------- 95, 97-98, 105-106
---------_--- 95-97


L l--------i- ----- ----- 101, 102; pl. 19


Page
Marine shore lines, general discussion of- -- ---- 99-101
Methods of study-- ------------------------97-98

Okefenokee shore line-------------- 99, 100, 101-102; pis. 19, 22-24
Orlando ridge----------------------------------- 102-103; pl. 19

Pamlico shore line-------------------- 99-100, 103-104; pls. 19, 25
Penholoway shore line --------- 96, 99
Phosphate deposits -------------------------------------____ 105-106
Purpose of investigation--------------------------- 95, 105-106

Recent coast line---------------------------- 100, 104; pls. 19, 21
References cited-------------------------------------- - 106

Silver Bluff shore line------------------- 99, 100, 104; pis. 19, 21
Stability, coastal ----------------------------------------- 105
Suffolk scarp-----------------------------------------_ 96-97, 105
Sunderland shore line and terrace -----------------_____--------- 96, 101
Surry scarp ----------------------------------__-- 96-97, 102, 105

Talbot shore line--------------------- --------------------- 96, 99
Tilting, continental ---------------------------------------. 105
Trail Ridge--------------------- ------ 96-97, 101, 102 ; pis. 19, 23

Wicomico shore line ------------ --- 99, 100, 102-103; pis. 19, 23


Lake Wales ridge-
















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GEOLOGICAL SURVEY


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AERIAL PHOTOGRAPH SHOWING WAVE-WASHED BARS ON THE OKEFENOKEE TERRACE, POLK COUNTY. FLA.
These bars were formed by marine abrasion of snall pronnontories of older terrain.






























31' . --'-" * - - ". - ..-. 31.






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PAMLCO SHORE LINE SCARP, AND LOWER PART OF WICO ...O TERRACE.
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