Excerpts from Origin of the Carolina Bays
The following text is from Douglas Johnson's work as presented in his book "The Origin of the Carolina Bays", Volume IV of Columbia University's Columba Geomorphic Studies series, pp 89 - 93.
Johnson is using these arguments to dismiss the meteorite impact theory. We see his observations as supporting our ejecta blanket hypothesis, where the bay depressions are imperfections in the surfacce of the blanket created during emplacement. The entire bulk of the sand statum in which the bays are contained is considered to be ejecta by us.
SIMMILARITY OF SAND IN RIMS AND IN BOTTOMS OF
BAYS
The reported similarity between
material in the rims and material in the bottoms of the
bays appears to be an inference based on occasional records
of sand encountered in drilling through the bay deposits.
If the inference were correct for the bays as a whole, it
would not seem to be significant of the origin of either
bays or rims since, no matter how these were formed, sand
in the rims could slump or wash or be blown into the
adjacent depressions.
It should be fully understood, however, that there is no
consistent similarity between material recently accumulated
in the bottoms of the bays and material in the rims. Both
types of deposit are abundantly described in many reports
of soil surveys throughout the bay country, and the
distinctions between them are made clear. The two are
mapped independently, named and described as different soil
types, and represented on maps by different colors. The
differences observed are not merely those due to the
presence of decaying vegetation within the marshy bays,
although the presence of clay, freshwater shells, and other
deposits does reflect the special conditions under which
the bay deposits were formed.
If Melton and Schriever meant to imply that the material
underneath the peculiar deposits of the bays, the
“bedrock” material in which the oval craters
were excavated, is essentially similar to that found in the
rims of the bays, then observations go throughout the bay
country as a whole indicate a situation altogether
different from that reported by these authors for the
Myrtle Beach area. Exposures in walls of many bays, in
near-by road cuts or shallow wells, in the slopes of
adjacent valleys cut below the levels of the bays, and in
the walls of artificial ditches dug for the purpose of
draining the bays (14) almost invariably reveal a strong
contrast between the material composing the Coastal Plain
deposits in which the craters are found and the superficial
sands of the bordering rims. Most frequently the Coastal
Plain deposits consist of sandy or clayey loam, usually red
but occasionally buff, pink, or purple, or a mottling of
these colors, more rarely, of gravel, orange-colored sand,
iron-cemented red or brown sands, marl, clay, and other
beds. Even where the Coastal Plain surface deposits are of
sand, one can usually distinguish readily between the
slightly clayey, less perfectly sorted sands of the plain
and the peculiar coarse, loose, white, gray, or faintly
buff sands of the oval rims. Only when recently wind-blown
sand forms a coating on the Coastal Plain sand is one in
doubt, and then the doubt relates to the possible
topographic development of a rim rather than to the
distinction between rim and plain material when both are
exposed in section.
In the Myrtle Beach area, conditions are somewhat unusual
because here the bays occur on a beach plain composed of
sand extensively reworked by wave action. But even here the
parallel beach ridges of sand alternate with swales in
which silt, clay, and marsh deposits are sufficiently
abundant to cause marked contrasts in vegetation and to
give muddy roads in which cars easily may be bogged. Yet
the rims consist uniformly of clean white sand; and the
silt and other material which should have been thrown out
to help form the rims, were these the product of meteoritic
impact, are not found in rim deposits. Prouty, (15) who
supports the meteoritic hypothesis, has recognized the
contrast between Coastal Plain deposits and the pure sand
of the rims, and has suggested that rain wash may have re
moved liner material from the rims, thus bringing about a
contrast in ejected rim deposits and underlying Coastal
Plain deposits which did not originally exist. There can be
no doubt that such separation does take place on the
Coastal Plain surface, giving a superficial layer of sand
quite unlike the underlying loam or similar material from
which it was derived. Weathering could, furthermore, easily
remove organic material from rims thrown up in such an area
as the Myrtle Beach plain. But there are serious objections
to applying Prouty’s suggestion to the rims in
general. If rims of red loam five, ten, and fifteen feet
high could be leached of their finer material and otherwise
altered to give white rims of pure coarse sand, adjacent
Coastal Plain ridges or swells of the same material should
similarly be leached; but these latter remain unaltered
close to the surface. Commercial sand pits excavated deeply
into the rims of white sand never, within the
writer’s experience, reveal an inner core of loam or
other material differing from the true rim of sand.
Drainage ditches cut through rims reveal not a gradation
from white sand above to red loam below but a sharp
contact, at the level of the adjacent plain, separating
pure white sand above from distinctly different Coastal
Plain deposits below. That the rims surrounding the oval
craters are uniformly composed of coarse white, gray, or
buff sand, regardless of what may be the color and
composition of the Coastal Plain beds in which these
craters are formed, is a fact fully established by abundant
field evidence. This fact seems to be fatal to any
hypothesis which would explain the rims as portions of the
Coastal Plain deposits ejected by the impact of meteorites.
Melton and Schriever in some measure appreciated the force
of this objection to the meteoritic hypothesis, for they
wrote: “In at least one respect the authors are not
convinced that the facts are adequate to substantiate
theory. In the rims thus far examined there is a noteworthy
absence of bed-rock fragments larger than sand
grains.”(16) But they pointed out that such fragments
might be found in the rims of bays not yet examined, that
perhaps such fragments should not be expected from the
unconsolidated, water saturated clastic sediments of the
Coastal Plain, and that, even if they did occur, the time
since formation of the bays might have been sufficiently
long for weathering to reduce such fragments to their
constituent elements.
With respect to the first point, it may be noted that
studies by Prouty and others, and the present
writer’s own extended examinations of bays in
seventeen counties of three states, fully substantiate the
observation of Melton and Schriever that “there is a
noteworthy absence of bed-rock fragments” in the
rims. Indian arrowheads and associated small fragments of
Hint and other materials used in making such arrowheads,
evidently of recent human importation, are the only
fragments larger than sand grains thus far reported.
With respect to the second point, it should be noted that
the Coastal Plain deposits include, close to the surface in
many places as well as in depth, layers of
well-consolidated, iron-cemented sandstone, beds of
limestone, coquina, silicified limestone and shell rock,
layers of chert, and other hard material. Large fragments
of bedrock are found on the slopes of shallow valleys and
ravines in areas where bays are present, and there appears
to be no reason why they should not have been ejected with
other rim materials if the rims were the product of
meteoritic impact.
With respect to the third point, the long period of
weathering invoked by Melton and Schriever is based on
their assumption that the bays are relatively ancient,
antedating the period of Coastal Plain terracing and the
formation of the Myrtle Beach plain with its parallel beach
ridges and swales. In an earlier chapter we have
demonstrated that this assumption of great age is invalid
and that the bays are of later date than the surface on
which they are found. Consequently, the opportunity for
weathering has been more limited than was supposed.
Furthermore, much of the material forming consolidated beds
in the Coastal Plain is of a nature to resist weathering
very effectively. Silicified shell rock found near the
surface in valley Walls and occasionally encountered in the
marshes of baylike depressions is extremely resistant.
Layers of even more resistant chert or of silicified
foraminiferal limestone are found close to the surface in
parts of the bay region, and the hard fragments are
collected by the natives for use in stone walls or as
decorations for flower gardens. All things considered,
there seems to be no reason to doubt that, if the bay rims
were the product of meteoritic impact, there would be an
abundance of bedrock fragments in the ejected material.
Thus the meteoritic hypothesis fails to explain
satisfactorily the striking contrast between the
composition of the Coastal Plain beds and the composition
of the rims, and the absence of bedrock fragments in the
latter.
(14) Bays showing red loam or other Coastal Plain beds
exposed in their walls are too numerous to record but not
all of these possess rims. Examples possessing rims and
showing contrasted Coastal Plain deposits exposed in bay
walls are: several small bays near Shell Bluff village,
center of Greens Cut quadrangle, Ca.»S_C.; bay northeast of
McBride Church, Hilltonia quadrangle, Ca.-S.C.; large bay
east of Blackville and hay 3 miles south of Elko, Williston
quadrangle, S.C.; Swallow Savanna Bay, Peeples quadrangle,
Ga.-S.C.; Coles Bay, Dial Bay, and Woods Mill Bay,
Mayesville quadrangle, S.C. Examples of bays possessing
white sand rims and known to he located in red loam or
other contrasted Coastal Plain deposits revealed in
neighboring road cuts, shallow wells, or valley walls are:
the oval bays on either side of the Little Salkehatchie
River, Olar quadrangle, S.C.; Sand Hill Bay, 2% miles north
of Elim, Florence County soil map, S.C.; Mossy Bay,
southeast of Blenheim, Marlboro County soil map, S.C.; Dial
Bay and associated bays previously mentioned, Mayesville
quadrangle, S.C.; small bay southwest of Sumter, on road to
Pinewood, S.C. Examples of bays in which the walls of
recently cut drainage ditches reveal red loam or other
Coastal Plain deposits overlain by sharply contrasting
white sand of rims are the bay northwest of McBride Church,
Hilltonia quadrangle, Ga.-S.C., and the Devil’s
Woodyard Bay near Springerville, north of Darlington, S.C.
(15) William F. Prouty, personal communication.
(16) A. Melton and William Schriever. The Carolina
“Bays” – Are They Meteorite Scars? Jour.
Geol., 41:52~66, 1933. See p. 65.