on the Geology of Fast Florida. 43 
of clearing for cultivation. Rocks are visible in only a few places, 
the principal of which is Ballast Point near Fort Brooke, at the 
head of the bay. This point has been much resorted to for pro- 
curing chalcedony of unusual beauty, formerly very abundant, 
but fine specimens are now rare. It coats masses of coral, a spe- 
cies of Astrea; which are derived from a Tertiary limestone, 
rising on the shore a few feet above high tide, and containing 
many. casts of bivalve shells and much silicified coral, which 
when broken exhibits a cavernous interior lined with chaleedony 
and sometimes with quartz crystals. Masses of chert are also 
very abundant in this rock; it contains casts and shells of bi- 
valves and univalves, differing from any I have observed in other 
rocks. They appear to be extinct species, and are, I believe, re- 
ferrible to the Eocene period; most probably to an upper division 
of that formation. I traced this rock to the Falls of Hillsborough 
river, nine miles above Tampa. It is here very full of casts and 
impressions of shells of species unknown to me... It forms the 
basis in this vicinity of the pine and hammock lands, and from 
the large admixture of fragments of the rock* with the soil, and 
the many masses of silicified coral scattered over the ground, it 
18 evident that the surface is nothing more than the disintegrated 
rock with just enough vegetable matter to nourish the trees and 
plants which grow thereon. In this spot, where there is so much 
lime in the soil, the pines are very lofty. There seems to the 
eye very little difference between the hammock and pine soils, 
both being light, sandy and unproductive. The poverty of the 
best fields I observed here is scarcely redeemed by the salubrity 
of the climate. On the Manatee river which enters Tampa bay 
on the southeast near its junction with the Gulf of Mexico, there 
1s a range of hammock land about fifteen miles long. The set- 
tlers here have a good opinion of the soil and propose to cultivate 
Sugar and tobacco. 'These hammocks depend upon the presence 
of the Florida limestone, which is certain to be the basis of the 
Shores of bays and rivers where the Post-pliocene formation of 
shells affords the lime which seems necessary to the growth of 
that tree in this region of barren soils. Of this formation there 
are two bluffs on the bay near Sarasota Point, as it is termed, 
+85 ' Found here an extinct species of Bulimus; B. floridanus, Con. 
