INSTITUTE OF SCIENCE, PHILADELPHIA. 63 



is at first sight difficult to distinguish between them, but close com- 

 parison in almost all instances reveals some constant characters by means 

 of which the two series can be separated. The number of clearly- 

 marked extinct species is, however, very great, and sufficient to fix 

 approximately, in default of direct stratigraphical evidence, the position 

 in the geological scale which the deposits occupy. This is, without 

 doubt, in the Miocene series, but just along what horizon it is difficult, 

 or even impossible, to determine. 



ROCKS OF THE MANATEE RIVER. The deposits exposed on the right 

 bank of the Manatee River at Rocky Bluff, a few miles above Braiden- 

 town, have been referred to in the narrative (p. 13) as consisting of a basal 

 marly limestone, and yellowish sandstone, and an overlying siliceous 

 conglomerate, almost totally devoid of fossil remains. The white marl, 

 on the other hand, is distinctly a shell rock, in which casts of fossils, 

 mainly bivalves, and their impressions, are exceedingly numerous. Among 

 these I recognized several forms distinctive of the Miocene formation of 

 the north, such as Pcctcn Madisonhis, P. Jcffcrsonius, Pcrna maxilla/a, 

 Venus ah'cata, Area idonca (?), etc., which left no doubt in my mind as to 

 the age of the deposit containing them. Fossils were much less abundant 

 in the accompanying yellow sandrock, but the species represented were 

 practically identical with those of the marl. The latter disappeared after 

 a comparatively short distance, but the sandrock continued in irregular 

 honeycombed ledges to the furthest point reached by us on the river. 

 The total elevation of the exposure is not more than three or four feet 

 above the river's surface. 



The discovery of a Miocene formation in this portion of the State was 

 not a little of a surprise, as it completely invalidated all the conjectural 

 ideas that had been framed relative to the geological structure of the 

 peninsula. It confirmed my impression as to the intermediate or equiva- 

 lent age of the beds occurring near Tampa, and clearly indicated what 

 would in all probability prove to be the true succession of the beds 

 further to the south. In other words, it was made manifest that this 

 portion of the State was neither that recent creation which the upholders 

 of the coral theory of growth had claimed for it, nor of that antiquity 

 which was assumed for it in virtue of the hypothetical extension of the 

 Oligocene beds. On the contrary, the evidence was conclusive that the 

 same physical forces which effected the formation of the newer Tertiary 

 series of the eastern border of the United States were similarly opera- 

 tive on the Gulf coast, and that the peninsula of Florida participated 

 in the same general movements that were known to have affected the 

 United States between Georgia and New Jersey during approximately 

 equivalent periods of time. In how far these movements were of both 



