GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK II5 



the Cortland!: series of intrusives belongs to Triassic time, although 

 exact relations to the Triassic beds in this case are obscure, and the 

 position of the Cortlandt series in the geologic scale is not definite. 



The make-up of the basal conglomerate and other lower beds of the 

 Triassic south of this quadrangle shows derivation from little modi- 

 fied rocks of Paleozoic age and indicates a very profound interval 

 of readjustment and erosion. Probably part of the West Point quad- 

 rangle was covered with Triassic or later sediments of Mesozoic age 

 which were later completely stripped by renewed erosion. The 

 Triassic deposition was probably preceded and certainly accompanied 

 and followed by great block faulting. Thus it happens that the 

 northwest boundary of this Triassic area is formed by a great fault 

 or series of faults, one of which .is continued into this quadrangle 

 as the west side of the Peekskill Hollow down-faulted block. 



That there was some deformation in the early stages of the 

 Triassic seems to be supported by the abrupt beginning of conglom- 

 erate made up of dominant limestone and quartzite pebbles undoubt- 

 edly derived from the exposed Hudson River- Wappinger-Poughquag 

 series which at that time must have occupied adjacent Highlands 

 ground. This period, therefore, was one of denudation of the area 

 under study, but' the sediments were not by any means the only 

 source of material for the Triassic beds. Some of them at the base 

 are very feldspathic and are very distinctly arkoses of disintegration 

 origin without much decay. As development continued, however, 

 alternating sandstones and shales accumulated with better sorting. 

 They probably represent destruction of the Hudson River-Wap- 

 pinger series as well as all the higher beds of Paleozoic Age which 

 now came for the first time within reach of erosion. Thus it hap- 

 pens that the material furnished is of different quality from that 

 found in the Hudson River shales proper or ir he bluestones of 

 the Catskills. Whatever of these later Paleozoic rocks may have 

 rested on the Highlands district were also carried away. 



Mesozoic faulting. By all means the most important develop- 

 ment, still preserved in this quadrangle, belongs to that portion of 

 Post-Paleozoic time known as Triassic and has to do chiefly 

 with block faulting. How much of the total faulting of the 

 district is of this age is again a matter impossible to determine in 

 any considerable detail, except in certain lines. For example, that 

 along Peekskill hollow enters the quadrangle at Tompkins cove, and 

 has such a relation farther to the south as to indicate beyond ques- 

 tion that it is a fault of this time. The one next farther to the west, 

 which has prominent development along the Hudson river, following 

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