154 
FLORIDA STATE GEOLOGICAL SURVEY. 
This consists of a mass of more or less water worn shells cemented 
by calcium carbonate. The amount of cement is seldom great enough 
to close the openings between the individual shells, though in some 
localities the process of cementation has proceeded far enough to 
produce a rather compact fossiliferous limestone. There is usually 
more or less sand present which is commonly in the form of thin 
laminae separating the shell beds, and various gradations from sand 
rock to shell rock may be noted along the Florida coast. (PI. VII, 
Fig- 2-) 
This rock was described by several of the earlier writers on the 
geology of the State. The following account is from a paper published 
by Jas. Pierce in 1825. 1 
Extensive beds of shell rock, of a peculiar character, occupy the borders of 
the ocean, in various places from the river St. Johns to Cape Florida. They are 
composed of unmineralized marine shells, of species common to our coast, mostly 
small bivalves, whole and in minute division, connected by calcareous cement. 
I examined this rock on the isle of Anastasia opposite St. Augustine where it 
extends for miles, rising twenty feet above the sea and of unknown depth. It 
has been penetrated about thirty feet. In these quarries, horizontal strata of 
shell rock of sufficient thickness and solidity for good building stone, alternate 
with narrow parallel beds of larger and mostly unbroken shells, but slightly 
connected. Hatchets are used in squaring the stone. Lime is made from this 
material, of a quality inferior to ordinary stone lime. 
The large Spanish fort, 2 and most of the public and private buildings of St. 
Augustine, are constructed of this stone. The rock extends in places into the 
sea, with superincumbent beds of new shells of the same character. 
Similar shell rock is found on the continent in several places. 
Of the organic Quaternary rocks Dali says: 
There is general opinion among the inhabitants, which was frequently 
expressed to me, in conversation, to the effect that between Tampa and the Keys, 
coquina-rock is only to be found at one place, the mouth of Little Sarasota Pass. 
But this idea is certainly erroneous, as at every projecting point of the Keys 
along the Gulf shore which we visited, I found traces of this rock, though often 
not visible above water, and frequently composed more of sand-grains than of 
shell, so that it looks much like wet loaf sugar. 3 
“Vermetus Rock”:—Another organic rock which has been de¬ 
scribed by Dali 4 is now being formed by colonies of a small gastropod 
Vermetus ( Petaloconchus) negricans. This organism secretes a 
skeleton in the form of a winding calcareous tube and when the tubes 
1 Pierce, James, Am. Jour. Sci., 1st ser., vol. ix, 1825, p. 123. 
2 The fort referred to is the one now known as Fort Marion. 
3 Dali, Wm. H., Geology of Florida, Amer. Jour. Sci., vol. xxxiv, 1887, pp. 
162-163. 
4 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey Bull. 84, 
1892, p. 153. 
