SECOND ANNUAL REPORT—STRATIGRAPHIC GEOLOGY. 
85 
same year Professor Allen 1 described both the limestone and “silex 
bed” at Tampa, and his account of these beds has been generally ac¬ 
cepted as correct. The same locality was subsequently visited by 
Tuomey. 2 In 1884, Kerr and Mitchell 3 visited Tampa and noted the 
replacement of fossiliferous limestone by chalcedony in what has since 
been called the “silex bed.” Ballast Point, near Tampa, where the 
“silex bed” is best exposed, is the locality where Bailey 4 found, what 
he regarded as infusorial earth, resting on the “silex bed.” Later in¬ 
vestigations have shown that this material is merely a residual ma¬ 
terial produced by the action of the weather upon the silicified lime¬ 
stone. 
In 1887, Heilprin 5 published an account of the explorations near 
Tampa and called attention to the fact that the fossil which Conrad 
regarded as a nummulite is really an orbitulite. Heilprin gave a brief 
description of Ballast Point and other exposures near Tampa, but 
does not appear to have recognized the relations between the lime¬ 
stone and the “silex bed.” Later publications by Dali give more com¬ 
plete descriptions of the Tampa exposures and show clearly that there 
are two horizons represented which he has called respectively “Tampa 
silex bed” and “Tampa limestone.” Because the “silex bed” is char¬ 
acterized by the presence of Orthaulax pugnax, Dali has called it the 
“Orthaulax bed” and the limestone has been designated “ Cerithium 6 
rock,” on acount of the presence of many specimens belonging to that 
genus. 
In his bulletin on the Neocene of North America, Dali 7 described 
the “Tampa group,” including what he designates the Tampa, Chipola 
and Alum Bluff beds. But the subsequent discovery of Orthaulax 
pugnax in the Chattahoochee led him to place the “silex beds” in his 
“Chattahoochee group .” 8 
While engaged in the field work for this report, additional informa¬ 
tion concerning the rocks at Tampa was obtained. Stated briefly, the 
observations showed the presence of a limestone below the “silex bed” 
1 Allen, Prof. John H. Amer. Jour. Sci., 2nd ser., vol. ii, 1846, pp. 36-48. 
2 Tuomey, M. Notice on the geology of the Florida Keys and the southern 
coast of Florida. Am. Jour. Sci., 2nd ser., vol. ii, 1851, pp. 390-394. 
3 Kerr, W. C., and Mitchell, Elisha. Scientific Society, 1884^5, p. 87. 
4 Bailey, J. W. Microscopic Observations, Smithsonian contributions to 
knowledge, vol. ii, No. 8, 1850, p. 19. 
3 Heilprin, Angelo. Explorations on west coast of Florida; Wagner Free 
Institute of Science Trans., vol. i, 1887, pp. 10 and 11. 
6 Dali, Wm. H. Neocene of North America, U. S. Geol. Survey, Bull. 84, 
1892, pp. 112-113. 
7 Loc. cit. 
8 Dali, Wm. H. Tertiary fauna of Florida; Wagner Free Institute of 
Science Trans., vol. 3, pt. 6, 1893, pp. 1564 and 1565. 
