H. P. Cushing — Lower Paleozoic Rocks of New York. 139 



On the Mercersburg quadrangle the basal 150-170' of the 

 Chambersburg limestone carries a fauna which, on the basis of 

 several identical species, among them Rliynclwnella plena, 

 Ulrich correlates with the upper Chazy (Valcour limestone) 

 of the New York section. This directly overlies the upper 

 Stones River (Pamelia), and just above it the Lowville fauna 

 comes in. Hence it follows that the New York Pamelia is, in 

 age, intermediate between the middle and the upper Chazy of 

 the Champlain Valley, and that there must be a break there 

 between those divisions. Also that the New York Chazy con- 

 sists of four divisions, Day Point, Crown Point, Pamelia and 

 Valcour limestones. And further, that Chazy deposition was 

 confined to the Champlain trough until Pamelia time ; that 

 then the northwest border was overlapped by the sea which 

 withdrew, at the same time, from the Champlain trough ; and 

 that, at the close of the Pamelia, the reverse oscillation took 

 place, the sea returning to the Champlain trough and with- 

 drawing on the northwest. 



Lowville and Black River Limestones. 



In their readjustment of the nomenclature of the New York 

 formations in 1899, Clarke and Schuchert gave the name 

 Lowville limestone to the formation previously called the 

 Birdseye.* Also, following the custom which had gradually 

 grown up in the State, they classed the darker-colored lime- 

 stones between the Lowville and the Trenton as Black Paver 

 limestone. This usage of Black River did not at all accord 

 with that of the early New York geologists, but was con- 

 venient and had gradually become customary. However, the 

 type sections of neither had received detailed study, and hence 

 they had not been precisely defined. 



In their areal mapping in the Watertown region in 1907-08 

 Gushing and Ruedemann found the typical, thin-bedded, dove 

 limestones of the Lowville to be overlaid by a thickness of 

 25-30' of thick-bedded, black, blocky limestone, above which 

 followed the Trenton. An uncomformity was also detected 

 between the black beds and the dove limestones. The black 

 limestones constituted a natural, lithologic unit, and we so 

 mapped them and called them Black River, this being the type 

 region of the formation. Subsequent study of the section in 

 company with Ulrich disclosed another break midway in the 

 black limestones, separating them into a lower portion with 

 much chert, and an upper in which chert was chiefly lacking, 

 and whose chief member is the massive, chertless bed known 

 as the 7 foot tier. That this upper break was a more con- 



* Science, Dec. 15, 1899. 



