SECOND ANNUAL REPORT-STRATIGRAPHIC GEOLOGY. 
155 
of a colony are seen united together they are thought to resemble coral, 
hence the local name “worm coral.” This rock is now being formed 
on the coast, and it doubtless extends back to the Pleistocene and 
possibly even to the Pliocene for Dali 1 reports the same species of 
gastropod from the Caloosahatchee marl. 
Yellow Sand :—With the Pleistocene is included a silty or clayey 
yellow sand which is widely distributed on the highlands in the central 
part of the peninsula. This material which is evidently the residual 
product left by the solution of the underlying rock is found on all the 
Oligocene formations and it probably began accumulating immediate¬ 
ly after the final emergence of these beds from beneath the sea. How¬ 
ever, much of the residual products of these rocks has doubtless been 
removed since the beginning of its formation and what remains most¬ 
ly represents* the results of weathering since the depression which 
resulted in the deposition of the marine Pliocene beds, but probably 
a portion of the deposit was formed during the preceding epochs. For 
convenience, it is all included under the Pleistocene. It was this ma¬ 
terial which Dali 2 described under the head of yellow sand, and from 
the analysis which he gives, the deposit appears to be about eighty 
per cent silica. Lime, which was presumably the most abundant con¬ 
stituent of the original rock, has dwindled to less than two per cent, 
but this condition is to be expected since the residuum of the weather¬ 
ing of limestone is the insoluble silica and silicates which existed as 
impurities in the original rock. 
Stratigraphic Position of the Pleistocene:—Where the contact be¬ 
tween the gray Pleistocene sands and the older formations has been 
observed, it is characterized by marked unconformity due to erosion. 
The relation between the gray and yellow sands has been observed 
at many localities and it is unconformable. The yellow sand appears 
to pass by gradation to the underlying Oligocene from which it was 
derived by weathering. The stratigraphic relation between the 
Coquina and the “Vermetus rock” and the underlying beds has not 
been observed but it is doubtless unconformable. 
With the exception of the yellow residual sand, the relation be¬ 
tween the various members of the Pleistocene and the overlying 
Recent deposits is conformable. In fact, the gradation between the 
Pleistocene and Recent beds often makes it impossible to differentiate 
between them. This is the case with the sands of Recent age, which 
are usually derived from the erosion and redeposition of the sands 
derived from the beds of Pleistocene age. Frequently the materials 
1 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey, Bull. 84, 
1892, p. 153. 
2 Dali, Wm. H., Neocene of North America, U. S’. Geol. Survey, Bull. 84, 
1892, pp. 154-156. 
