LOWER SILURIC SHALES OF THE MOHAWK VALLEY 3! 



This is, among others, suggested by an outcrop at Crescent, at the 

 last bend of the Mohawk. At the latter place an anticline brings 

 to the surface (thereby causing the rapids in the river) about 50 

 feet of " bluestone " (a calcareous sandstone) of the type charac- 

 teristic of the " Frankfort " (Schenectady) beds, in beds 2-3 feet 

 thick with intercalations of black shale. The latter, however, do 

 not furnish the " Frankfort " f aunule, noted in a later chapter, but 



Corynoides calicularis Nicholson 

 Cf. Azygograptus ? simplex Rued. 

 Diplograptus putillus Hall 

 Climacograptus bicornis PI all 

 Diplograptus cf. angustifolius Hall 

 Leptograptus annectans Walcott (narrow form) 



This congeries of forms contains on one hand the Corynoides on 

 account of which we refer the beds to the Canajoharie formation, 

 a reference which is supported by the close position of the outcrops 

 to the belt of Canajoharie beds at the mouth of the Mohawk. It 

 also contains Leptograptus annectans, a species that 

 to our knowledge has been found hitherto only in the basal Utica 

 beds in the neighborhood of Trenton, N. Y., and in the true Utica 

 beds of Cincinnati (title 61, page 265) but the form repre- 

 senting this species at Crescent is not strictly the same as the typical 

 Holland Patent type. The lithologic features of this interesting 

 outcrop also indicate the fact that in the east, the upper portion of 

 the Canajoharie formation may assume the lithologic character of 

 the "Frankfort" (Schenectady) beds, a fact that would argue for 

 a direct succession of the two formations in this region. 



While the Canajoharie shale is eastward in the Mohawk valley 

 cut off by the Hoffman's Fault, we have found it to reappear north 

 of Schenectady along Alplaus creek and thence the black shales can 

 be traced past Ballston Spa, Saratoga and along the edge of the 

 Precambric to Glens Falls, where they are again cut out by faults. 

 The locality on Alplaus 1 creek has afforded: 



Corynoides calicularis 



Glossograptus quadrimucronatus mut. cornutus 



Lasiograptus eucharis 



Leptobolus insignis 



Orthoceras hudsonicum nov? 



1 A curious distortion of the old German locality name " Aalplatz," 

 eel-place. 



2 This species retains in pyritized condition the protoconch and nepionic 

 portion of the shell. See note, p. 113. 



