1915.] NATURAL SCIENCES OF PHILADELPHIA. 567 



Cardiff to the east, but overlapping it and coming in contact with 

 the Marcellus to the west. 



Theoretical Considerations. 



If the points outhned above are admitted, a number of questions 

 immediately arise. The first to be considered is this: How far 

 westward does the overlap type of structure persist? If it extends 

 to the western limit of the State involving each higher unit in turn, 

 it is clear that younger and younger material will come to lie in 

 contact with the basal black shale. Much depends upon the deter- 

 mination of the western equivalent of the Mottville. Should it 

 prove referable to the Stafford limestone,^^ the present writer could 

 not escape the conclusion that the Stafford of western New York 

 is the equivalent of the lowermost Skaneateles of the central portions 

 of the State. In such a case the Stafford of western New York 

 separates not the Marcellus from the Cardiff, but the Marcellus 

 from the bulk of the Skaneateles formation. 



If, on the other hand, the overlap westward goes no farther than 

 Cayuga Lake, we may be dealing with a north and south axis of 

 Onondaga limestone, on each side of which the shale units are repro- 

 duced in a similar stratigraphic succession. Though this view is 

 well within the bounds of possibility, it can hardly be said that the 

 known examples of the Onondaga-Marcellus contact furnish evidence 

 in its support. 



Opportunity has not yet been found for anything like a thorough 

 paleontological study of the Mottville beds. The species so far 

 identified reveal a fauna not unlike that of the Stafford. It is 

 believed, however, that correlation based upon fossils alone is most 

 unsafe in determining the position of these Mottville strata. 



Returning to the stratigraphic aspects of the problem, it may be 

 said that overlap in the structural sense can hardly be questioned. 



1^ In this connection see N. Y. State Museum Bulletin 49, p. 120, where occurs 

 the following statement by Dr. John M. Clarke: 



"In the outcrops along Criss creek, 2^ miles south of Union Springs, the 

 strata above the horizon of the Agoniatite limestone are shown, and a point of 

 interest in this section is the presence of a bed of 1.5 feet of blue and olive cal- 

 careous shales, lying above the general mass of darker shales, which carries 

 certain trilobites (Homalonotus, Phacops), brachiopods, gastropods, etc. per- 

 taining to the normal Hamilton shale fauna. These shales he at about the 

 proper horizon of the Stafford limestone, though no trace of this rock has been 

 seen so far east." 



There can be little doubt that Dr. Clarke is describing the upper limy portions 

 of the Mottville which are exposed in this creek. It is perhaps unnecessary to 

 add that, in the matter of Stafford correlation, one could hardly look to a more 

 authoritative source. 



