LOWER SILURIAN SYSTEM OF EASTERN MONTGOMERY CO. 423 



with very rare birdseyes " sharply separated from the underlying 

 Calciferous.^ 



Black river limestone. In the earlier works on New York geology 

 the Black river limestone was either not separated from the succeed- 

 ing mass or was confused with other rocks. In the final report on 

 the first district (1843) Mather gives the following synonomy of 

 the Black river limestone: " IMohawk Hmestone, Birdseye limestone, 

 base of the Trenton limestone, Bald mountain limestone, Blue lime- 

 stone, Chazy limestone. Black marble of Isle la Motte, Seven foot 

 tier^ and perhaps the Neeleytown limestone, of the geological 

 reports of New York^ MetalHferous limerock, Transition chequered 

 and sparry limerocks of Eaton, No. 2 of the Pennsylvania survey."^ 



In the final report of Vanuxem the Black river limestone is clearly 

 distinguished and described at its type locality. Black river in Jeffer- 

 son county. The description is in part as follows : 



The cHff which forms the western margin of this river con- 

 sists generally of a limestone in thick layers^ the upper ones 

 unusually thick. . . The mineral character is generally the 

 same with the Birdseye, specially the layers below the upper surface 

 one, being rather brittle and breaking with a smooth and 

 flat conchoidal surface. . . The upper part is intermixed 

 irregularly with black shale and exhibits the characters and 

 position of the mass intermediate to the Birdseye and the Trenton 

 limestone of the Mohawk which position it also holds. . . The 

 large and handsome chambered Columnaria sulcata 

 [Columnaria alveolata Goldfuss] , the same which is found 

 in the thick layers resting upon the Birdseye at Tribeshill, etc. is 

 often seen in the exposed surface of this rock.^ 



In reference to the rock having the stratigraphic position of the 

 Black river Hmestone in the IMohawk valley he says : 



On the ]\Iohawk there are several quarries opened in a mass of 

 limestone which rests upon the Birdseye as may be seen in three 

 of them, and in two of which it is followed by the well characterized 

 Trenton limestone. This mass therefore holds the same position 

 as the upper division of the Black river limestone and contains some 

 of the same fossils, but the mineral character is different, resembling 

 more the gray limestone of the upper mass of the Trenton limestone. 

 These quarries are Stanton's on the south side of the Mohawk about 



^13th annual report N. Y. state geologist, 1893, p. 422, 423. 

 "Geology of New York, pt 1, p. 402. 

 ^Geology of New York, pt 3, p. 42. 



