148 PALAEONTOLOGY OF NEW YORK. 



NOTE ON THE BLACK SLATE SUCCEEDING THE HAMILTON LIMESTONES AT THE FALLS 



OF THE OHIO. 



The Black slate, known under that name alone, in the vicinity of New 

 Albany, Jeffersonville, and many other places in the southern part of Indiana, 

 has been recognized in all the published sections of the strata at the Falls of 

 the Ohio. It has usually been regarded as of Devonian age, but has sometimes 

 been claimed as belonging to the Carboniferous series. Evidences of its true 

 geological age and its equivalency with known sedimentary formations in the 

 east must be sought in its fossil contents and its geological relations, since its 

 direct continuity cannot be traced. 



In order to come to this point with some preliminary appreciation of the 

 subject, it may be remarked that the results of all our geological investigation 

 have shown a gradual (occasionally an abrupt) thinning, in a westerly and south- 

 westerly direction, of all the sedimentary formations which lie between the 

 Upper Helderberg limestone and the base of the coal formation. In New York 

 and Pennsylvania, these are represented by coarse and fine shales and sand- 

 stones, the coarser materials predominating. At intervals there occur beds, 

 greater or less in extent, of fine sandstone, slate or shale ; and these become 

 more marked and conspicuous in a westerly direction ; while gradually the 

 arenaceous deposits give way, and the whole mass becomes finer in character 

 and'greatly diminished in its aggregate thickness. In the course of several 

 hundred miles, not only do the arenaceous, littoral portions of the deposit 

 give place to finer sedimentary materials, but calcareous matter supervenes, 

 either as a general admixture with the shale, or as continuous belts of distinct 

 concretions, or of concretionary or other forms of limestone bands, forming an 

 important feature in the geology. 



Although a full discussion of the different conditions in which these deposits 

 present themselves in their westward extension would occupy much more space 



age of (ha Hamilton group, associated with OHhis sulmrbicularix, Attypti n tinihin.% A. curpera, Kumnphaliut 

 cycUistomugt etc. This is about the same horizon in which Hall found his Megistocriwcs latus." 



This is the only reference of any of these fossils to the Hamilton group which I have been able to find 

 among the writings of Lyos and Cakkkday, or of Major Lyon. 



