LOWER SILURIAN SYSTEM OF EASTERN MONTGOMERY CO. 42 1 



Mohawk valley (p. 417-22). The formation is said to have a thick- 

 ness of " 200 to 250 feet on the Mohawk " (p. 418). It is also 

 stated that " the fucoidal layers are near the summit of the forma- 

 tion." Speaking more in detail of this member of the Calciferous 

 the author Mr Darton says " The fucoidal layers of Vanuxem are 

 a characteristic member of the Calciferous over a wide area. They 

 are well exposed in many of the quarries along the Mohawk, where 

 they are worked extensively for building stone. . . The member 

 consists of a fine grained, thick bedded limestone intermediate in 

 character between the typical Calciferous and Birdseye deposits with 

 intercalated streakings, blotchings, reticulations and sprinklings or 

 mixtures of coarse sand and Calciferous materials of light color in 

 greater part but weathering dark. The alternations are in thin 

 layers at varying but frequent intervals, and the bedding of the fine 

 grained material is usually more or less disjointed into a partial 

 breccia. The coarse materials are disposed in forms suggesting 

 fucoids, and this resemblance has given the name to the member. 

 Fossils are usually present and constitute a limited but characteris- 

 tic fauna. This member appears to have a thickness of about 15 

 feet in the Mohawk valley " (p. 420, 421). 



Birdseye limestone. The name " birdseye " or " birdseye marble " 

 was a popular designation of limestone containing cylindrical tubes 

 which in cross section on the polished surface bore a fancied resem- 

 blance to birdseye maple. Prof. Eaton uses the term in its popular 

 sense in the following mention of the rock now known as Birdseye, 

 "when it [metalliferous limerock=Trenton] is compact and con- 

 tains numerous stylastrites, as on East Canada creek it may be 

 wrought into a beautiful variety called birdseye marble.^" In the 

 Geological nomenclature of North America birdseye marble becomes 

 a designation of the subdivision of the metalliferous limerock (Tren- 

 ton) in which " the natural layers are pierced transversely with 

 cylindrical petrifactions so as to give the birdseye appearance when 

 polished " (p. 13). In another place he speaks of these vertical 

 tubes as " vertical encrinites " (p. 23). 



In the First annual report on the geological survey of the third district 

 (1837) by Mr Conrad, the Birdseye limestone is called "gray sparry 

 limestone of the Mohawk valley." Its thickness is given as 30 feet 

 at Littlefalls and it is said to thin out and disappear to the east along 



^Geological and agricultural survey, district adjoining Erie canal, p. 32. 



