40 Geology of Tampa Bay, Florida. 
are seen swimming about; from the number of fish, I inferred 
that they are fond of dcsipuentinie sulphureted waters. When I 
visited this spring, the stream flowing from it into the Hillsboro’ 
river was literally crowded with them. ‘These springs are very 
abundant; there is a small one southwest of the fort, near the 
western shore of the bay, and a large one about seven miles east ; 
some species of shell fish live in the streams that flow from them. 
A species of Neritina, that is very abundant in the brackish waters 
at the head of the bay, seems to have a great predilection for 
these sulphurous waters, in which the individuals grow to a great- 
er size than they attain elsewhere. 
There is a peculiar beauty and placidity in the springs of Flor- 
ida, embosomed as they are with a perennial foliage, that might 
well have confirmed the Spanish adventurer Ponce De Leon in 
the belief that some one of them possessed the power of removing 
the decrepitude of age, and restoring the freshness and elasticity 
_ of youth. 
Along the shore of Tampa Bay, the country is low, seldom at- 
taining a height of more than ten feet above the surface of the 
water; it is generally sandy, but in some places there are beds of 
marl, which when they form the surface, constitute a rich and 
fertile soil. These beds differ materially in their composition 
and organic contents; they evidently belong to different geolo- 
gical periods. One of the most ancient and interesting of these 
deposits can be seen about two miles west of Fort Brooke, where 
a section a few hundred feet in length has been exposed by the 
ing of the waters of the bay. Immediately back from the 
shore it is covered by three or four feet of loam and sand. This 
bed consists of blue marly clay, interlaminated with seams of 
carbonate of lime, which probably has resulted from the decom- 
position of shells; that which renders this deposit unusually inter- 
esting is the remarkably beautiful petrifactions that it contains, 
and that surpass any thing of the kind I ever saw. Interspersed 
throughout the marl are masses of silex presenting a great variety 
of shapes and colors; some have a rough and jagged surface and 
wine yellow color, some are hollow cylindrical tubes of different 
colors, straight or bent, from one to six inches in length, and from 
one fourth of an inch to one inch in diameter, with a fine drusy 
interior ; others are beautifully agatized, having that moss-like 
arance that agates sometimes ‘possess ; these silicious concre- 
tions are both. opaque and translucent, and are probably of organic 
