254 BE W YORK PA L^EONTOL OGY. 



Since the Spirifera gregaria and Sp. acuminata are characteristic fossils of the 

 Corniferous limestone in all the western localities, it is clear that the hydraulic, 

 siliceous and crinoidal beds of the sections in the vicinity of Louisville have 

 thinned out, and are represented only by the few inches of oxide of iron which 

 has accumulated at this place during the deposition of the limestones in other 

 localities. In other sections, however, the oxide of iron is represented as 

 lying between the Hydraulic limestone and the Black slate, showing a lapse 

 of time and the absence of some member of the series ; but in nearly all the 

 sections, the Hydraulic limestone, with its associated or equivalent beds, is 

 represented in greater or less force, the thickness varying from a trace, to six 

 or eight or even twelve feet in the counties of Scott and Jefferson ; while in 

 some localities in Clark and Floyd counties, it reaches a thickness of twenty 

 feet or more. 



In a general section of the geological formations of Clarke and Floyd 

 counties, given in the Report of 1873, Prof. Cox doubtfully refers the Crinoidal 

 and Hydraulic limestones to the Hamilton group : * 



Knob limestone— Keokuk group 80 feet. 



KX^^'l^-hook group 344 feet. 



}' 



Knob shale, J 



New Albany Black slate, 



Crinoiilal limestone, J-(?) Hamilton group 140 feet. 



Hydraulic limestone, ) 



Corniferous limestone — Upper Helderberg group 22 feet. 



Utica limestone — Niagara group 52 feet. 



Magnesian limestone— Clinton group 30 feet. 



Madison limestone — Cincinnati group 207 feet. 



In the Report of 1874, p. 123, Prof. Cox gives the relations of the New 

 Albany black shale with the superincumbent rocks, indicating it as the equiva- 

 lent of the Genesee shale of New York. 



* Report of 1873, p. 172. Since this reference does not appear in succeeding reports, the view then 

 entertained may have subsequently been modified. This section had escaped my attention in looking for 

 authorities regarding the age of the upper limestones of the Falls of the Ohio, and should have been cited 

 in its proper place in the preceding pages. 



