34 NEW YORK STATE MUSEUM 



rather to a group of three formations. The Black River group, as 

 now recognized by the Survey, comprises the Lowville, Watertown, 

 and Amsterdam limestones and of these only the Lowville and 

 Amsterdam limestones appear to be present in the lower Mohawk 

 valley. The missing Watertown corresponds to the well known 

 Black River limestone of the Black River valley. Because of the 

 thinness and small areal extent of the Black River-Trenton lime- 

 stones they are shown together on the accompanying geologic map. 



Lowville limestone. The Lowville (former "Birdseye") 

 formation is commonly present within the map limits, but it is never 

 more than a few feet thick. The following description of this 

 limestone by Darton^ for the Mohawk valley well applies to the 

 Broadalbin district : " The Birdseye is in greater part an im- 

 palpably fine-grained, light dove-colored limestone more or kss 

 filled with dark-colored, vertical, columnar fucoidal stems. It 

 weathers to white or a light ash gray tint, which is an especially 

 characteristic feature. Owing to its very fine grain and compact 

 structure its fracture is smooth or conchoidal and the texture of 

 the rock is rather brittle. The ends of the dark fucoidal stems 

 which are spotted over the surface of the bedding planes resemble 

 birds' eyes, and from this feature the [old] name of the formation 

 is [was] derived. It is in moderately heavy, regular beds and has 

 a vertical cleavage [jointing]." The so-called fucoidal stems have, 

 in recent years, been referred to the genus Tetradium of the 

 branching corals. Within the map limits these stems are replaced 

 either by calcite or sandy clay and are not always present. 



The Lowville is well exposed at two points on Kennyetto creek 

 two miles east of Broadalbin where a few feet of the typical rock 

 may be seen in layers less than a foot thick and containing rather 

 imperfect coral stems. In the vicinity of Kegg's quarry, east of 

 Cranberry Creek, the rock is well developed showing a thickness 

 of a few feet of dove-colored, very compact limestone with many 

 large, yellowish, vertical coral stems. Near the limekiln these beds 

 are seen to alternate with dolomitic beds which bear a close resem- 

 blance to the Little Falls dolomite. Similar alternating beds are 

 also shown close to the map edge east of Mayfield. Along the 

 eastern border of the Black River-Trenton area at Galway the Low- 

 ville is thinly present but the exposures are not so good. In a 

 quarry beyond the map limit and two miles south-southeast of 

 Perth several feet of typical Lowville beds are exposed. 



The Lowville is always thin (generally under ten feet) in the 



1 47th An. Rept. N. Y. State Mus. p. 616. 



