6 GEOLOGY OF ERIE COUNTY 



organisms from sea water and built up into their skeletons, or the 

 minerals originally dissolved in sea water but deposited because of 

 the drying up of the water containing them. The detrital rocks 

 in Erie county are shales and sandstones. These shales represent 

 both deep-sea and off-shore deposits of mud and fine silt, and 

 perhaps, also, marsh deposits at sea-level. The sandstones are 

 nowhere (extensive enough in Erie county) to warrant the belief 

 that they were beach deposits. They are, like the shales, 

 off-shore sea-bottom deposits of fine detritus and sand. The great 

 limestone formations of northern Erie county represent two 

 methods of deposition. First, the Bertie limestone with the 

 underlying shale seems to have been laid down, partly at least, by 

 the precipitation of the minerals in sea water consequent upon 

 the drying up of the water containing them. The great deposit 

 of Onondaga limestone in the northern part of the county is the 

 accumulation of carbonate of lime abstracted from sea water by 

 corals, crinoids and molluscs, and of silica by sponges, diatoms 

 and other organisms. 



Fig. 1. Diagram to show how the southerly dip of the rocks of Erie 

 county bring those exposed at the surface in the northern part far 

 below the surface in the southern part. 



All the rocks of Erie county dip to the southward, those in 

 the northern part at the rate of about twenty five feet in a mile, 

 those in the southern part probably at a greater inclination. As 

 a consequence of this southward dipping, rocks which crop out 

 at the surface at the northern edge of the county are brought by 

 this inclination deep below the surface in the southern part. 

 Thus the Onondaga limestone, which is encountered in northern 

 Buffalo when cellars are being dug, is reached in drilling for gas 

 at Orchard Park at from 600 to 700 feet below the surface, and 

 at the northern bank of Cattaraugus creek at 1925 feet. Only 

 part of this depth is due, however, to the inclination of the 

 strata. Part is due to .the difference in altitude between Buffalo 

 and the other two places. : . _ 



