208 
FLORIDA STATE GEOLOGICAL SURVEY, 
of the peninsula or around the shores of the islands that foreshadowed 
the peninsula. The quartz grains no doubt halted to form beds of 
sand, sandy marl and even sandy limestones many times in their jour¬ 
ney from their original ledges to the south end of the peninsula. They 
were worked over again and again and even roughly concentrated in 
this southward drift, so that the mass of siliceous material at the south 
end of the peninsula represents the removal and assortment of many 
times its bulk of quartz-bearing rock. The process of concentration 
apparently continued through the Miocene and Pliocene periods, a suf- 
ficent length of time for the accumulation of hundreds of feet of sandy 
material. Only a depression of the coast, and the substitution of off¬ 
shore for near-shore deposits would interrupt the process. There is 
no evidence of such interruption in the sands under Key Vaca. 
PLEISTOCENE. 
UNEXPOSED PLEISTOCENE FORMATIONS. 
Of Pleistocene formations earlier than the limestones and sands to 
be described, the only positive evidence at hand is that of well samples. 
A few records show a considerable thickness of Pleistocene material. 
Thus a bed of coquina at a depth of 118 feet in a well at Delray yielded 
twenty-four species of mollusks and two of corals (non-reef builders), 
of which ninety per cent, were identified as Recent by T. Wayland 
Vaughan, indicating that the age of the coquina was early Pleistocene, 
earlier than the Miami oolite. Few samples have been taken from 
other east coast wells between depths of 100 and 200 feet. Samples 
from the well on Key Vaca showed reef rock to 105 feet. At Key 
West limestones, evidently of shoal water origin, are indicated by the 
samples from the deep well, but the thickness of Pleistocene beds 
earlier than the surface oolite is uncertain. On the west coast rather 
fine quartz sand underlies the Postmans River limestone at Everglade. 
This sand is at least forty feet thick. No samples were saved from 
the deep well at Marco and but few from the wells at the mouth of 
Caloosahatchee River. The latter, except the Buck Key well, show 
sands and marls to a depth of over 100 feet. 
The notable feature of the well records is the reported finding of 
sands and unconsolidated material below hard rock at widely separated 
localities. Samples from West Palm Beach, fifty-five to seventy-five 
feet, show much worn shell fragments cemented, and replaced by crys¬ 
talline calcite, with pockets or beds of quartz sand, but no hard rock 
close to surface. Samples from Miami show much the same variety of 
material below the surficial oolite. 
