CHAPTEFw 111. 

 Surface Geology. 



Drift ; hurled valleys ; lake-basins ; soils. 



Glacial Erosion. — Wherever the upper surfaces of hard 

 rocks are exposed on the uplands, they are seen to be grooved 

 and polished by the passage of the Northern Ice Sheet in the 

 Glacial Epoch. The amount of erosion is uncertain ; but from 

 such isolated peaks as Elk Mountain, Ararat, and Sugar 

 Loaf — the summits of which were islands in the Jler de 

 Glace, and thus escaped its action — the outlook over the 

 surrounding country, lying from 500' to 1000' beneath, sug- 

 gests the thought that much of it may have been removed 

 by ice. 



2200' A. T. is the greatest elevation at which I have ob- 

 served direct evidence of glaciation, either in the shape of 

 morainic debris or striated rock surfaces. All higher sum- 

 mits which I have examined are destitute of Drift deposits. 



South 20° west (mag.) is the general direction of the 

 scratches, or stria3, on the hard Catskill sand-rocks.* There 

 are exceptions to this course, however, where the ice cur- 

 rent appears to have been deflected locally. 



The Northern Drift. — Deposits of morainic debris are 

 found all along the streams ; cover much of the highlands, 

 and remain on many of the hill slopes where the latter are 

 not so steep as to have shed them subsequently. 



The material is heterogeneous ; consisting usually of both 

 rounded and angular bowlders of sandstone, of shale, of 

 limestone, and of the peculiar calcareous breccias of the 

 CatsJcill ; and intermixed with all these we often And a 

 large amount of clay. 



*This direction is in marked contrast to that of the striw at the western line 

 of the State (see Q 2 Q 5 Q, 1 ) where the glacial grooves generally tend S 20° E. 



(25 G 5 .) 



