II P. disking — Lower Paleozoic Rocks of New York. 143 



Amsterdam limestone. — There is present in the eastern Mo- 

 hawk sections and the Saratoga region a limestone of Trenton- 

 ish aspect, which the early geologists were clear sighted enough 

 to distinguish from the typical Trenton. Conrad called it the 

 Mohawk limestone ; but this term was variously used by the 

 different geologists, was hence abandoned in the final reports, 

 and instead the formation was referred to as " base of the Tren- 

 ton " limestone. The rock is chiefly in the third district, and 

 that most excellent geologist, Yanuxem, discusses it in his 

 chapter on the Black River limestone, with which he classes it 

 notwithstanding the name used.* "We propose to call it the 

 Amsterdam limestone. It has of late years been usually refer- 

 red to as Trenton, both along the Mohawk and at Saratoga, 

 but is older than anything in the type section at Trenton Falls, 

 and is properly referable to the Black River, forming the 

 youngest division of the group in New York. It is also a de- 

 posit in a different trough from that of the type Trenton and, 

 during Amsterdam time, the entire western border of the Adi- 

 rondacks was unsubmerged. The Amsterdam is emphatically 

 a deposit of the eastern and southeastern border only. On 

 the southeast (eastern Mohawk and Saratoga) it rests on the 

 Tribes Hill or Little Falls and is followed by shaly limestones 

 and shales, or simply by shales. In the Champlain valley true 

 Trenton limestone overlies the Amsterdam, though even here 

 only the lower Trenton consists of limestone. In the lower 

 Mohawk region the bulk of the true Trenton consists of shale, 

 with some thin, intercalated limestone bands in the lower por- 

 tion. 



The view here urged in regard to this formation is nothing 

 but the old view of Conrad and Yanuxem, and a new term is 

 proposed for the formation because of the confusion attending 

 the use of the term Mohawk limestone in the Annual Reports, 

 and its ultimate abandonment by the proposers; and also to 

 avoid conflict with Clarke and Schuchert's useful and more 

 comprehensive term Mohawkian.f The type sections are 

 along the Mohawk in the vicinity of Amsterdam. 



The shales. — Above the Black River or the Trenton lime- 

 stones black shales follow, in all the New York sections. In 

 the Champlain region limestone deposit continued through 

 the lower Trenton, but the upper Trenton is represented by 

 shales, with occasional thin limestone bands; in the eastern Mo- 

 hawk and Saratoga sections the shales follow the Amsterdam, 

 and the entire Trenton consists of shales except for the imme- 

 diate base which consists of alternating, shale and thin lime- 

 stone bauds; in the western Mohawk sections there is again a 



*Geol. 3d Dist., pp. 43-5. \ Science, Dec. 15, 1899. 



