568 PROCEEDINGS OF THE ACADEMY OF [DeC, 



That is (1) a fossiliferous zone is separated from a black shale by a 

 bed of barren gray shale, (2) followed west the fossil zone is seen to 

 approach nearer and nearer to the black shale in successive sections, 

 (3) at the west the fossiliferous zone lies immediately above the 

 black shale. 



Such relations at least suggest an unconformity somewhere in the 

 series. The writer has, however, failed to discover positive evidence 

 of one in passing from the Onondaga to the Mottville. It is true 

 that the base of the Mottville limy layer is frequently very uneven. 

 The same observation likewise holds for the Agoniatites limestone. 

 Both cases are, however, regarded as due to a concretionary struc- 

 ture; limy segregations merely pushing downward into the strata 

 below. 



When considered in relation to the general black shale problem, 

 it is believed that the data obtained in this area go to strengthen the 

 theories which explain the Marcellus as an invasion from the east 

 and south toward the north and west.^^ On the other hand, trans- 

 gression over a land surface is somewhat questionable; in fact, the 

 evidence rather points to a different conclusion. We are apparently 

 justified in regarding the Marcellus as a formation Avhich, so to 

 speak, runs diagonally across the geologic column, its lower layers 

 and more eastern portions being contemporary with some Onondaga 

 to the west while its upper and more western portions were probably 

 deposited at a time when Cardiff sedimentation was occurring to 

 the east. 



Evidence presented by Kindle^^ shows that black shale (presumably 

 Marcellus) deposition in the Allegheny region was taking place at 

 the same time with Onondaga accumulation. For the particular 

 area here studied it is sufficient to call attention to the thin black 

 shale intercalations which are found in the Onondaga south of 

 Union Springs. The very gradual transition from Marcellus to 

 Cardiff and the general structure outlined in these notes both argue 

 for partial contemporaneity between Cardiff and Marcellus. 



Explanation of Plate XXII. 



Diagram showing the stratigraphic relations exhibited by the Mottville member 

 in passing from Cayuga Lake on the west to the TuUy quadrangle on the east. 



i« Clarke, John M., N. Y. State Museum Bulletins 49 (pp. 115, 137) and 52 

 (pp. 668-9). 

 UMch, E. O., and Schuchert, Charles, N. Y. State Mus. Bui. 52, p. 665. 

 Grabau, A. W., N. Y. State Mus. Bui. 92, p. 231. 

 "Principles of Stratigraphy," pp. 407, 424. 

 " Kindle, E. M., U. S. G. S. BuUetin 508. See especially pp. 10, 25, 54. 



