GEOLOGIC FORMATIONS OF NEW YORK 155 



portion is generally a dark gray slaty rock, with layers of impure 

 limestone, well seen along the Auburn and Syracuse railroad. 

 The important salt springs of Syracuse being derived from these 

 rocks, they received originally the name of Onondaga salt group. 



In the days of the original Natural History Survey, the salt 

 was not found in solid masses, though the gray part of" the rock 

 in some places showed impressions of the peculiar ' hopper 

 shaped ' crystals of halite or rock salt, proving that it once ex- 

 isted there in small quantities. It is now known to be diffused 

 in beds and lenses through large extents of these strata, through 

 which in places the surface water percolates and bears the salt 

 in solution to the deep basin at Salina. This was found, by bor- 

 ing, to be several hundred feet in depth, filled with gravel and 

 sand, in which the salt water seemed to lie as in a reservoir, and 

 from which it is raised by the pumps for the supply of the evap- 

 orating works. The Onondaga lake, which is a comparatively 

 shallow body of fresh water, lies over this deep mass of gravel, 

 but has a water tight bottom of marl which keeps its fresh 

 waters separate from the salt waters below. 



During the past 18 years a large industry has been developed 

 from the boring of salt wells in New York state at points dis- 

 tant from Syracuse, at Warsaw and in the Genesee valley. These 

 wells show that rock salt in beds and lenticular masses varying 

 in thickness from a few inches to 150 feet is abundantly interca- 

 lated between the layers of shale and limestone of the Salina 

 group. .This salt being easily soluble in water does not appear 

 at the surface qf the ground nor within reach of surface waters. 



The upper drab or gray shales of this group contain great 

 quantities of gypsum, which is quarried extensively from Madi- 

 son county westward. The rock over the masses of gypsum often 

 seems arched, as if this mineral, in forming, through some chem- 

 ical change, had exerted an upward pressure, lifting the overlying 

 masses. 



The whole group is remarkably destitute of organic remains; 

 not a single fossil having been found in the lower part or red 

 shale, and but a small number in the upper portion at a few 

 localities. 



