124 FLORIDA state; geological survey. 
at Arcadia. 1 The close resemblance of these marls to the Caloosa- 
hatchee marl seems to warrant regarding them as a phase of that for¬ 
mation, thus making ‘‘Arcadia marl” a superfluous term in geologic 
nomenclature. . 
Stratigraphic Position-:—The contact of the' Caloosahatchee marl 
with the underlying Miocene has not been observed, but there is a 
considerable change in fauna between the Miocene which is probably 
due to physiographic changes which may have permitted the erosion 
of the Miocene beds before the beginning of the Pliocene deposition. 
The contact of the Caloosahatchee marl with the. overlying Pleisto¬ 
cene is commonly marked by an erosion unconformity. Where this 
unconformity is not noticeable it has been masked by reworking of 
the Pliocene marl by the waves of the Pleistocene sea. 
Lithologic Character: —- The Caloosahatchee marl consists of a 
light-gray shell marl which is often interbedded with nearly pure sand. 
The matrix is usually very calcareous, but locally it consists of sand 
and even in the most calcareous portion sand is abundant. The shells 
are remarkable for their excellent state of preservation and their 
abundance in certain layers makes it possible to secure excellent col¬ 
lections. 
Thickness:—It is difficult to form a correct estimate of the thick¬ 
ness of the Caloosahatchee marl, but its maximum is probably about 
twenty-five feet. Single exposures seldom exceed five to ten feet, and 
the average thickness is probably less than eight feet. On the whole 
the Caloosahatchee marl is probably to be regarded as thin, though it 
may thicken considerably toward the central portion of the peninsula 
and toward the southern end of the State. 
Physiographic Expression:—The Caloosahatchee marl occupies a 
region of such low altitude that it has been only slightly dissected. In 
fact, with the exception of the valleys of the streams entering Char¬ 
lotte Harbor the surface of the region-underlain by this formation is 
an almost unbroken plain. While this is doubtless in part due to the 
later deposit of Pleistocene sand, it is doubtful if the surface of the 
Caloosahatchee marl has ever been greatly eroded. 
Paleontologic Character:—Dali’s list of Pliocene fossils obtained 
from the Caloosahatchee marl in Florida includes 639 species, of which 
256 species are not known from other States. The marine formations 
of this period are very fossiliferous, and the fauna as a whole is such 
as might be expected in shallow water. Since the Caloosahatchee marl 
was the only Pliocene formation known in Florida at that time this 
number may be taken as a measure of the species recognized as be- 
Ibid. pp. 132-133. 
