1915.] NATURAL SCIENCES OF PHILADELPHIA. 561 



THE STRUCTURAL RELATIONS OF SOME DEVONIAN SHALES IN CENTRAL 



NEW YORK. 



BY BURNETT SMITH. 



The shale mass which intervenes between the Onondaga and 

 TuUy hmestones of central New York was formerly separated into 

 a lower division of Marcellus shales and an upper division of Hamilton 

 shales. It is now pretty generally conceded that this classification 

 is inadequate to express the facts and the geologists of the State of 

 New York now employ Marcellus shale, Cardiff shale, Skaneateles 

 shale, Ludlowville shale, and Moscow shale in describing the strati- 

 graphic units encountered in passing upward from the Onondaga 

 to the Tully. These shale units by inference correspond with 

 definite subdivisions of the Devonian time scale. They are also 

 regarded as possessing a rather wide east and west distribution 

 across the State. ^ Recent field studies in Onondaga and Cayuga 

 Counties have convinced the writer that the lower members of the 

 shale mass have a far from simple history. Followed in an east 

 and west line they present changes which remain unrecognized even 

 in the recent classifications. These notes are therefore submitted 

 as a partial record and preliminary interpretation of the observations 

 made. 



A brief survey of the general stratigraphy brings out the fact 

 that the shales have been deposited upon Onondaga limestone. 

 In some places the line between the Onondaga and the succeeding 

 black shale is quite sharp, but at others there is a transition zone of 

 limestone and black shale alternations in thin bands. Great varia- 

 tions in the amount of limestone intercalation are noticed in the 

 10 or 15 feet just above the Onondaga. One limestone stratum, 

 however, is shown in all good exposures. This layer known as the 

 Agoniatites limestone is about 3 feet in thickness and holds a position 

 approximately 10 or 15 feet above strata which are referable to the 

 Onondaga. Lying thus upon black shale or upon black shale and 

 limestone alternations the Agoniatites limestone is in turn followed 

 by a deposit of dense black shale in which concretions of large size 

 are apt to be a very conspicuous feature. This higher black shale 



1 N. Y. State Museum Handbook 19, Table 2. 



