1915.] NATURAL SCIENCES OF PHILADELPHIA. 563 



associated fossiliferous shales above and below which are exposed 

 along the Skaneateles outlet south of Mottville.'' This member 

 can be readily recognized by its lithologic and paleontologic char- 

 acters for a few miles east and west from the type section. Eastward 

 there is some slight change in its features, but the horizon can be 

 traced with little difficulty onto the Tully quadrangle where the 

 writer considers it to be identical with the basal layers of the Skane- 

 ateles formation up to and slightly above the limestone band already 

 mentioned.^ 



The presence of a thin fossiliferous zone between masses of rela- 

 tively barren shale is usually regarded as a matter of some paleon- 

 tologic interest and the Mottville is no exception in this respect. 

 It was not, however, until the writer studied the relations of this 

 member to underlying formations westward that he realized the 

 important position which the Mottville holds in any attempt to 

 solve the stratigraphy of the lower shale units. 



Its authors recognized that the Cardiff shale thins toward the 

 west, a statement to that effect appearing in their description of the 

 type sections.^ 



Nevertheless, the writer confesses that he was much surprised to 

 learn in the field that the gray shales between the harder limy por- 

 tions of the Mottville and the black Marcellus thin down to about 

 100 feet southeast of the village of Marcellus (Skaneateles quad- 

 rangle), to about 50 feet in the belt south of Shepard Settlement, 

 to about 25 feet near the western limit of the Skaneateles quadrangle, 

 and to about 15 feet on the eastern shore of Cayuga Lake (Auburn 

 quadrangle). 



As stated above, the top of the Cardiff in the type locality has 

 been defined by its authors as being 20 feet below a limestone band 

 in their Skaneateles. The writer regards this limestone band as 

 the equivalent of the upper limy portions of the Mottville, and if 

 this correlation is correct there is very little room for a Cardiff 

 formation between the harder Mottville and the Marcellus of the 

 Auburn quadrangle. It is therefore believed that (in the absence 

 of positive diagnostic characters) the Cardiff shale cannot be differ- 

 entiated as a separate unit west of the Skaneateles quadrangle. 



• At the Mottville locality about 10 feet of shale are exposed below the crinoidal 

 band. In other sections an additional 10 or 15 feet of fossiliferous strata are 

 usually to be seen at the base. These latter beds, though not exposed at the 

 type locality, are included in the term Mottville as used in this paper. 



* The above refers to the Skaneateles formation as described by Clarke and 

 Luther; see N. Y. State Museum Bulletin 82. 



9 X. Y. State Museum Bulletin 82, p. 45. 



