390 On the Geology of the Florida Keys. 
Arr. XLIII.—WNotice of the Geology of the Florida Keys, and 
of the Southern Coast of Florida ; by M. 'Tvomey, Prof. Geol., 
University of Alabama. 
Dvrine the past summer, [ paid a short visit to the coast of 
Florida, with the view of comparing the recent deposits there, 
with the white limestone of Alabama. This limestone occurs in 
the latter state in a stratum two or three hundred feet in thick- 
ness, composed for the most part of irregular grains of carbonate 
of lime, sometimes but slightly cohering, but frequently suffi- 
ciently hard to fit it for a building material. It abounds in 
fragments of corals, but the most conspicuous fossil, on account 
of the vast numbers in which it occurs, is Orbitoides Mantelli. 
This fossil, so far as I know, is not found east of Alabama, and 
certainly does not extend into South Carolina. Echinoderms and 
corals are found in great abundance wherever the white limestone 
occurs. It has been traced from Mississippi to the Cape Fear 
river above Wilmington ; throughout the entire distance, whilst 
the stratum varies in thickness, its mineral composition con- 
tinues unchanged-—a white and nearly pure carbonate of lime. 
Towards Virginia it becomes more siliceous, the corals and 
echinoderms disappear, but the other fossils for the most part are 
identical. 
Some specimens of white calcareous mud from Florida, which 
I saw in the cabinet of my friend, Prof. Gibbes, of Charleston, and 
which, when dried, presented nearly the same appearance as the 
white limestone, lead me to suppose that there exists, at this 
moment, in the Gulf of Mexico, conditions similar to those under 
which the tertiary white limestone was deposited. 
The recent limestone from the West India Islands, so frequently. 
brought as ballast by vessels, is seen on all our wharves, and is 
familiar to every one; but I did not know till I reached Key 
West, that at all the Keys between that and Key Biscayne, the 
sands on the shore, and the very mud on the bottom of the “a 
e 0 
readily to the axe, with | 
nehes on the surface 
