CHAPTER VII. 



BLACK SHALES OF OHIO— GENESEE SHALES OF NEW-YORK. 



By this name a series of black bituminous shales are designated, 

 which in the States of Ohio and Indiana are found in immediate 

 superposition on the limestones of the Helderberg series, and which 

 in the north part of the Michigan peninsula rest on the beds of the 

 Hamilton group, as do the Genesee shales of New York, which are 

 generally considered the equivalent of the black shale. 



By their lithological character, the black shales approach the 

 shale and sand-rock beds of the Waverly group next succeeding 

 them. 



A change of the ocean bed, causing a total change in the [mate- 

 rial of the deposits, had already begun while the black shales were 

 forming ; but the fossils inclosed within the shales, and in a series of 

 shale and sandstone beds above them, in the so-called Portage and 

 Chemung group, exhibit a yet greater affinity to the fauna of the 

 subjacent limestone formation than to the fauna of the incumbent, 

 lithologically nearer related beds of the subcarboniferous shale 

 and sandstone formation. This is the regular order, in the suc- 

 cession of strata, within the State of New York, and as in the 

 States of Ohio and Michigan a similar order in the character of the 

 rock beds resting on the black shales was observed, they were 

 naturally supposed to be the equivalents of the Portage and Che- 

 mung group. 



By the study of the fauna found in the upper part of this arena- 

 ceous shale formation above the black shales in Michigan, Prof. 

 A. Winchell came to the conclusion that those of the Chemung 

 and Portage groups had a different character from the com- 

 plex of fossils found in the supposed equivalent Michigan strata, 

 which latter he declared emphatically to be of carboniferous type. 

 He selected for this upper arenaceous rock series the name of 



