LOWER SILURIC SHALES OF THE MOHAWK VALLEY II 



■ In 1901, the author (title 47) in his bulletin on the Hudson River 

 beds near Albany, correlated the Normanskill shale with the lower 

 Trenton and argued on this account for the suppression of the 

 term Hudson River group. He also pointed there (page 560) to 

 the decrease of the thickness of the Trenton limestone eastward in 

 the Mohawk valley and the rapid increase of the " Utica " shale in 

 the same direction. In the following years the author also showed 

 the presence of graptolite zones ranging from the top of the Cambric 

 through the Beekmantown and Trenton to the Utica in the Hudson 

 River shales. A broad belt of shales on the west side of the Hud- 

 son overlying the middle Trenton shales and Normanskill shales was 

 still referred to the Utica shale ; and the shales at Cohoes and to the 

 west of the Utica belt were in accordance with Hall and Vanuxem 

 correlated with the Frankfort division of the Lorraine group, 

 mainly on the ground of a series of small lamellibranchs obtained 

 about Cohoes and of the supposed upper Utica aspect of the Dudley 

 Observatory faunule. 



In 1902 Paleozoic Seas and Barriers in Eastern North Amer- 

 ica by E. O. Ulrich and Charles Schuchert was published. This 

 very important paper, which apparently has not been sufficiently 

 understood or appreciated by many, has helped greatly in the 

 elaboration of the complex shale problems by pointing to the exist- 

 ence of separate troughs or channels in the shale region (the Chazy 

 and Levis troughs) of New York and to the draining of these 

 channels independently of each other. 



Clarke in the Classification of the New York Series of Geologic 

 Formations (title 52) discarded the term Hudson River and dis- 

 tinguished the Utica shale and Lorraine beds as stages of the Cin- 

 cinnatian ; the Frankfort shale, Pulaski and Salmon River being con- 

 sidered as "early terms applied to the local development of these 

 beds in central New York." 



In an excellent description of the Geology of Little Falls, Gush- 

 ing (1905) pointed out the presence of 100 feet of passage beds 

 between the Trenton and Utica. He says : " Lithologically these 

 beds are no more Trenton than they are Utica but are distinctly 

 intermediate in character, and no more to be classed with the one 

 formation than with the other." He mapped them as a distinct 

 unit, and in a later communication to Professor Miller (title 65, 

 page 21) he proposed the term Dolgeville shale for these passage 

 beds, considering them a formation " as a shaly eastern repre- 

 sentative of the upper Trenton limestone of the type section." 



