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NEW YORK STATE MUSEUM 



southern part of the county lying along the east side of the 

 Genesee valley, are located on the southeast side of drift hills, 

 while those on the west side are on the southwest side of 

 the hills. Several large gravel deposits at the sides of the 

 valley, for example, the one used by the Buffalo, Rochester & 

 Pittsburg Railroad, at Scottsville, were probably formed by 

 large streams debouching into the deeper water of a glacial 

 lake once filling the valley. 



The clay deposits of the county are found in low lying areas 

 or depressions. The most extensive lies at the foot of the Pin- 

 nacle range and extends with irregular narrowing outline 

 southwest along the Genesee. 



The peat deposits lie in depressions formed by stream erosion 

 or by the irregular deposition of the drift. 



The location of the marl deposits, like those of the peat, may 

 be either in natural depressions in the drift or in basins formed 

 by stream erosion. These deposits are of two kinds: those 

 formed by precipitation from hard water and those resulting 

 from the accumulation of the shells of fresh-water mollusks. 

 The former are limited to the regions underlain by the Salina 

 and Onondaga formations. Their origin is due to the large 

 amount of calcareous shale and limestone in the drift, from 

 which the water derives its lime. The latter are not limited in 

 their distribution and usually occur beneath peat deposits. So 

 far as known, they are comparatively shallow. 



Rochester, having a population of upward of 163,000, or over 

 three fourths that of the entire county, is. so far as the areal dis- 

 tribution of these natural products permits, the center of the 

 various industries based on them. 



Quarry industry 



All the important or regularly worked quarries of the county 

 are within the limits of Rochester. The Lockport dolomite 

 which underlies the greater part of the city furnishes 99^ of 

 its house foundations. The remaining material is either shipped 

 into Rochester or comes intermittently from two or three small 

 quarries in the Medina sandstone northwest of the city. The 

 last is of little importance. 



