Geology of Seneca County. 



105 



water's edge, as near as ascertainable, along the western line of 

 the county : 



FORMA.TION. 



Thickness. 



Distance. 



Dip 

 per mile. 



Salina 



Upper Helderberg 



1,000 

 I 160 



1,100 



250? 



6 (+10) 

 10 

 9 



62 



Marcellus 



16 



Hamilton 



122 



Upper Devonian 



33 







Mean 



2,510 



42i 



60 







Omitting the Salina and measuring obliquely from McQuane's 

 (Upper Helderberg) to the S. W. corner of the county, we have 

 the same result, viz.: \^j\J = 60 feet dip per mile. 



Clay, Brick, Tile. 



Most of the clay in the county is included in the belt previously 

 described, and is of glacial origin. It was deposited when the 

 lakes were much higher than at present ; a condition generally 

 referred by geologists to the closing periods of the Ice- Age. In 

 a wider sense, all the clay of this region, including late deposits 

 in isolated hollows, is " glacial," inasmuch as its particles must be 

 derived from the general covering of till. 



A distinction is necessary between the clays of the Hudson 

 Kiver region and those of central and western l^ew York in 

 this latitude. Of the former it is noted that the upper layers are 

 yellow ; from Syracuse to Buffalo the same layers are deep red. 



The under clay, in Seneca county, is called '' blue " by those 

 who make brick and tile, but the name is applicable only by a 

 technical fiction. The color is simply a lighter red, varying in 

 shade. "When burnt, however, it turns a light buff, while the 

 top, or "red" clay, turns red, increasing in darkness as it is 

 longer baked. This difference doubtless arises from the presence 

 of a considerable amount of lime carbonate (and magnesium 

 carbonate), which has been removed by leaching from the upper 

 layers. 



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