1144 NEW YORK STATE MUSEUM 



known as the " gray cement." Directly beneath the Rondout, 

 or " gray cement/' the Cobleskill is found. The Cobleskill about 

 the cement mines in Ulster county is known as the " middle lime- 

 stone ledge " and separates the Rondout, or " gray cement/' from 

 the underlying Salina waterlime locally known in Ulster county 

 as the " black cement." 



In the quarries and mines at Rondout the Cobleskill is repre- 

 sented by a thin layer of limestone 7 inches thick. This layer, 

 separating the Rondout from the Salina, weathers to a gray color 

 and is characterized byRhynchonella ?lamellata Hall 

 and a species of Leperditia. Southwestward from Rondout the 

 Cobleskill thickens rapidly and at Whiteport it is 10 feet, at 

 Binnewater 12 feet and at Rosendale 15 feet. The Cobleskill also 

 thickens northward from Rondout, and at East Kingston it is 

 found to have a thickness of 10 feet. The Cobleskill was also 

 observed near Glasco, where some specimens of Proetus sp. 

 undet. were collected. It also is seen in the vicinity of West 

 Camp and northward toward Catskill. 



In the Rosendale- Whiteport cement region Darton 1 has 

 referred to the Cobleskill, or " middle limestone ledge," as 

 follows : 



There are two cement beds in the Rosendale- Whiteport region, 

 and at Rosendale the lower bed, or " dark cement," averages 

 about 21 feet in thickness, and the upper bed, or " light cement," 

 11 feet, with 14-15 feet of waterlimestones intervening. 



In the cement region south of Whiteport there are two cement 

 beds, the upper, or " white cement," having a thickness of 12 feet 

 and the lower, or " gray ( = black or dark) cement," 18 feet with 

 17-20 feet of waterlime beds between them. 



The Cobleskill limestone in the Rosendale-Whiteport region con- 

 tains an immense number of corals and other species character- 

 istic of this formation in Schoharie county; but Darton did not 

 give any account of its " coralline " character in this section. As 

 will appear later, the Cobleskill in the vicinity of Rondout seems 

 to have been included by Darton with the Manlius or Tentacu- 

 lite limestone. 



The Salina waterlime, or " black cement," is best developed at 

 Rosendale, where it has a thickness of 22 feet, at Binnewater it 



1 N. Y. State Mus. 47th An. Rep't. 1894. p. 528, 531. 



