﻿Il8 NEW YORK STATE MUSEUM 



that neither the bottom nor the top beds of the series are to be seen 

 in this locality. 



The region is one of considerable relief representing preglaeial 

 erosion. The glacial drift mantle has modified it chiefly by obscur- 

 ing some of the smaller irregularities of rock contour, and espe- 

 cially by partially filling many of the stream gorges. Postglacial 

 erosion has not completely reexcavated the old channels. But the 

 contour of the uplands reflects the character of the bed rock with 

 considerable success. The tendency of the more massive and coarse 

 grained varieties of rock to resist weathering and erosion more suc- 

 cessfully than the finer grained and more argillaceous or shaly 

 facies is a general characteristic. Since these varieties form suc- 

 cessive or alternating beds throughout the whole area, the result is 

 an almost universal cliff-and-slope surface form. This bed rock 

 topography is somewhat obscured but not wholly obliterated by 

 glacial erosion and deposition. Therefore it may be used with con- 

 fidence in locating or tracing the more durable beds since they 

 almost invariably appear as a shelf or terrace with a steep margin 

 toward the lower side and a gentle slope on the rising side. 



Structural features 



The rock types include bluish gray or greenish gray sandstones 

 with almost horizontal bedding, and sometimes exhibiting cross- 

 bedding structure, and compact very dark argillaceous shales. These 

 two are of about equal prominence, but only the sandstone is of 

 importance in the present discussion. Its minute structure will be 

 given in greater detail in the petrographic discussion. 



Jointing is common and persists in two sets nearly at right angles 

 to each other — one striking northeastward and the other toward 

 the northwest. In some of the best exposures, these joints are 

 clear-cut and run 10 to 18 feet apart, dipping almost vertically. In 

 the more massive beds there is very little small jointing, so that the 

 character is especially favorable to large dimension work. 



But still more prominent structures are the partings which follow 

 the bedding planes. These give the rock a decided tendency to 

 cleave naturally into slabs, the uppermost exposed portion of almost 

 every outcrop exhibiting this slab structure in more or less perfec- 

 tion. So general is this structure at all horizons in the sandstones 

 of the series that there can be no doubt of its connection with 

 some original sedimentation character. Besides it is a potential 

 factor in nearly all the beds even when not very apparent. The 



