INSTITUTE OF SCIENCE, PHILADELPHIA. 



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both banks. Mr. Willcox also obtained fragments of a silicco-calcarcous 

 rock, containing numerous casts and impressions of one or more forms 

 of sea-urchin, from a small island situated about three miles' southeast 

 of the mouth of the Homosassa River. One of the species (the most 

 abundant form) is, I believe, without question the Pygorliynchus Gonldii 

 of Bouve (Proc. Boston Soc. Nat. Hist, Dec., 1846; Ibid., Jan., 1851. 

 Nudcolitcs Mortoni of Conrad, Journ. Acad. Nat. Sciences Phila., II, 

 p. 40), from the older Tcrtiaries (Oligoccne?) of Georgia. The same 

 species was subsequently identified by McCrady in the limestone of 

 Alligator (Columbia Co. ?), Florida, and by him referred to a new genus 

 Ravcnclia (Proc. Elliott Soc. Nat. Hist., Charleston, March, 1858). 



ROCKS OF THE TAMPA BAY AND HILLSBORO REGIONS. Two distinct 

 kinds of rock appear at Ballast Point, on Hillsboro Fay, at about water 

 line, rising in most places not over two feet above it, still oftener less, 

 and at Newman's perhaps three or four feet. The one rock, a highly 

 fossiliferous yellow limestone, is manifestly in place, and forms the bed 

 of the beach, shelving at a moderate angle beneath the waters of the 

 bay. It contains numerous impressions of the Venus penita described 

 by Conrad in 1846, and large numbers of the singular foraminifer referred 

 by this paleontologist to Nummulites (A r . \_Nemophora\ Floridamts). It is 

 very remarkable, in view of the abundance and perfection in which the 

 fossil occurs at this locality, that an imperfect or abnormal specimen, 

 misleading in the details of its structure, should have served as a type 

 for a description and illustration of the species. 



The rock containing this supposed nummulite has generally been 

 referred to the Vicksburg group, but as far as paleontological evidence 

 goes, I see no valid reason for considering it to belong to this age. 

 None of the distinctive Oligocene fossils of the formation occur in the 

 rock, nor did we find in it any traces of the foraminifcral types so char- 

 acteristic of the Oligocene region of the northern part of the peninsula. 

 On the contrary, all the fossil forms occurring here appear to be distinct, 

 except in so far as they are represented in the second kind of rock above 

 referred to, and in the rock corresponding to it which forms the bed of 

 Hillsboro River. If Oligocene, the rock in all probability represents a 

 horizon higher than the Vicksburg beds and the Florida " Nummulitic " 

 (or Orbitoitic), but the evidence is all but conclusive for considering it 

 Miocene, and as the near equivalent of some of the beds of the island of 

 Santo Domingo. I failed to detect in the rock any traces of distinctively 

 Miocene fossils; but the association near by of an indisputable Miocene 

 deposit leaves little room for doubt as to the absolute relationship. 



The second form of rock found at Ballast Point is of much firmer 

 consistency than the limestone, and appears in large, rounded or angular 



