804- NEW YOKK STATE MUSEUM 



Tlie Lower Helderberg rocks of Onondaga county are mostly 

 dark blue and fine grained, occurring in beds 1 to 5 feet thick. 

 Tliey weather to a bluish gray. Most of them are fairly pure 

 but at times contain some magnesia or clayey material. The 

 pure beds are the important lime producers and are used for 

 structural work in the county. 



Two beds of hydraulic limestone lie near the top of the group, 

 and according to Luther are often separated by 4 feet of impure 

 limestone. In the eastern part of the county the upper layer is 

 4 feet thick, but it pinches out in the Splitrock quarry west of 

 Syracuse to reappear again near Marcellus Falls, where it is 2 

 feet 10 inches thick in Watkins quarry, and reaches 4 feet in 

 Oorrigan's quarry at Skaneateles. As at the latter place it is 

 only separated from the lower bed by a shaly layer, the two 

 practically form one bed 9 feet 6 inches thick. 



At Manlius the beds are separated by 4 feet of blue lime- 

 stone and at Street's quarry near Onondaga Hill by 1 foot 8 

 inches, at Marcellus Falls by 1 foot 7 inches, and at Skaneateles 

 they are together. 



Luther gives the following thicknesses for the lower waterlime 

 layer in Onondaga county. 



FEET INCHES 



Manlius, J. Behan's quarry 4 



Jamesville, E. B. Alvord 4 



Brighton, Britton and Clark 5 



Skaneateles, Corrigan's quarry 5 



At Splitrock the upper member occurs in the southeastern part 

 of the quarry but is wanting in the western portion, its place 

 being occupied by a 9 foot bed of blue limestone. 



The hydraulic limestone in Onondaga county is brittle, com- 

 pact, fine and even grained. It is dark colored with a conchoidal 

 fracture but weathers to a light color. The beds are generally 

 well defined but do not as a rule contain any fossils. The rock 

 was discovered in 1818 in connection mth work on the Erie 

 canal. As in other cases attempts were made to burn the stone 



