88 
FLORIDA STATE GEOLOGICAL SURVEY. 
Ballast Point the fauna of the “silex bed/’ though largely marine, con¬ 
tains many fresh water shells which were probably supplied from some 
lakes or lagoons situated near the shore. The complete list of the 
fossils from the “silex bed” is given by Dali, who says d 
About forty-nine per cent of the species in the Orthaulax bed are peculiar 
to it, and very few of the more minute forms which should be present in such 
a fauna are known. The relations of the fauna are most intimate with that 
of the Oligocene beds above it, the Orbitolite or Tampa limestone, the Chipola, 
and the Oak Grove sands. With either of these the percentage of species 
common to both is more than twice as great as with any of the beds below, 
such as the nummulitic, the Peninsular limestone, or the Vicksburg. But it must 
be admitted that the faunas of all these, except the last, are very imperfectly 
known. With the faunas of the horizons above the Oak Grove sands, there is 
little in common, though in the tropical waters of the Antilles, about eight per 
cent of the species are believed to survive to the present day. Only about 2.6 per 
cent survive except in tropical waters. 
One of the most interesting features of the fauna is the assembly of land 
shells, which are southern immigrants and have left no survivors on the Am¬ 
erican continent at the present day, though representative species occur to the 
southward. 
The fauna of the limestone in the Tampa formation contains fewer 
species than that of the “silex bed,” but the faunas are closely related, 
as will be seen by the following quotation which contains Dali's com¬ 
ments on the list of fossils from these two beds : 1 2 
Total, ninety-five species, of which thirty-six are uncertain specifically, leav¬ 
ing fifty-nine identified, of which thirty-seven are common to the silex beds, ten 
are peculiar to the Tampa limestone horizon, four are known from the Ocala 
nummulitic limestone, and two appear in the Vicksburgian, the Jacksonian, and 
the Claibornian. One species (and probably more not yet discriminated) sur¬ 
vives into the Chipola and two are believed to persist to the recent fauna. 
' Structure:—The Tampa formation lies near sea level and hence 
it is difficult to get sections which show the structure of the beds. 
Apparently the formation is nearly horizontal with a slight seaward 
dip. While the formation may be affected by gentle flexures, the 
evidence is still too meager to show their existence. 
Local Details:—The “silex bed” of the Tampa formation is best 
exposed at Ballast Point where it rises only a few feet above tide. At 
this locality the maximum thickness of the bed is not shown. Dali’s 3 
section at Tampa is: 
1 Dali, Wm. H., Geological results of the study of the Tertiary fauna of 
Florida; Ex. from Trans. Wagner Free Institute of Science, Phila., vol. iii, 
Part vi, p. 1565, 1903. 
2 Ibid, p. 1572. 
3 Dali, Wm. H. Neocene of North America, U. S. Geol. Survey, Bull. 84, 
1892, p. 113. 
