GLACIAL GEOLOGY OF THE COHOES QUADRANGLE II 



rock with a slope to the east of 80 feet in a distance of 2 miles. 

 This is a part of the old valley floor, though now reduced by 

 erosion. 



In somewhat sharp contrast to the system of valley depressions 

 thus far described are the uplands portions of the quadrangle. The 

 uplands, as here referred to, stood above the level of inundation by 

 the glacial waters and are clearly marked off from the area covered 

 by waters both in respect to topographic features and the materials 

 of which the soils are composed. The Pleistocene deposits filling 

 the valley depressions, although now trenched by the great river 

 courses and ravined by the minor streams, still represent, especially 

 where deltas have been developed, the general level of the body of 

 waters in which they were laid down. The uplands stand out in 

 marked relief above this level. This contrast is very striking in 

 the field when one stands at a point commanding a view of the two 

 topographic regions. 



The surface of the uplands is in general highly irregular. This 

 is due primarily to the structure of the underlying rocks and to 

 the effects of differential erosion upon the rock surfaces in pre- 

 glacial times. The rocks are shales and sandstones of the Cambric 

 and Ordovicic series and possess the folded structure and altera- 

 tions due to metamorphism common to these rocks as they occur 

 in the Hudson valley region. The strike of the folds is in a general 

 north-south direction and this gives to many of the hills an elon- 

 gated form, with long axes trending north and south. Two of the 

 highest elevations, Rice mountain and Mount Rafinesque, in the 

 middle portion of the southern third of the quadrangle, are, how- 

 ever of irregular, massive form. The highest elevation of surface 

 is near the southeastern corner of the sheet where a ridge of 

 steeply inclined strata attains the height of 1265 feet. 



The surface of the uplands bears evidence of considerable modifi- 

 cation by ice agencies. Many of the hills which show exposures of 

 rock have somewhat even and smoothed outlines indicating the 

 effects of abrasion by moving ice. In many cases the more 

 smoothed surfaces face north, indicating the wear of the rock on 

 the side from which the ice approached. In some instances low 

 hills of topographic form approaching that of drumlins are found 

 to be reduced rock hills, partly covered by glacial till. The group 

 of hills west of the Saratoga battlefield near the northern edge of 

 the sheet is of this character. 



In general, the minor topographical aspects of the surface ot 

 the uplands are due to deposits of glacial origin, a description of 



