LOWER SILURIC SHALES OF THE MOHAWK VALLEY 15 



Canajoharie beds), the East Canada creek one from the Trenton 

 through the transition beds into the lower Utica, while Moyers 

 creek at Frankfort and the " Gulf " at Ilion give excellent sections 

 through the Frankfort shale but fail to show its base. No continu- 

 ous Utica section has been found in the neighborhood of Utica; 

 the name according to Vanuxem is derived from the exposures in 

 the Starch Factory creek (page 58, " a creek to the east of the 

 city"), now largely, within the city. The most important of these 

 sections are here discussed in detail. 



" UTICA " SHALE OF .AUTHORS 1 



The belt of black "Utica" shale that follows the south side 

 of the Mohawk valley is cut off by the Hoffman Ferry fault, as 

 is well shown in the geologic map of the Amsterdam quadrangle by 

 Prosser, Cumings and Fisher, to be replaced by an area of " Hudson 

 River " or " Frankfort " beds that occupies nearly all Schenectady 

 county and toward the east merges into the zone of folding. Just 

 west of this fault, between Hoffman Ferry and Amsterdam, the 

 south bank of the river is formed by cliffs of Little Falls dolomite 

 and Trenton, above which, according to Prosser and Cumings, the 

 contact of the Trenton and " Utica " is seen in several places, which 

 have been visited by the writer. 



In the Swartztown creek section (title 45, page 472; title 44, 

 page 457) two feet of black partly noncalcareous, but mostly cal- 

 careous shale 2 is exposed overlying very fossiliferous Trenton. The 

 contact in this section which is the first west of the Hoffman Ferry 

 fault is disconformable and the surface of the Trenton irregular. 

 The fossils are : 



Corynoides calicularis Nicholson 

 Dicranograptus nicholsoni var. parvulus nov. 

 Diplogr. (Mesogr.) mohawkensis nov. 



A mile farther west is a section opposite Cranesville (title 33, 

 page 653) in which about 21 feet of basal Trenton, over- 

 lying the Amsterdam limestone (formerly Black River) with 



1 It will be shown in this paper that both the Utica shale and Frankfort 

 shale of the lower Mohawk valley are of another, earlier, age than hitherto 

 supposed. They will therefore, in distinction from the true Utica and 

 Frankfort shales, be cited in quotation marks, until differently named. 



2 The " Utica " shale is described as calcareous in distinction from the 

 Frankfort shale. The two have therefore been distinguished by Professor 

 Prosser in the field by the use of the acid bottle. 



