GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 23 



The Inwood limestone and Manhattan schist lie in the southeast 

 part of the quadrangle. The limestone lies almost east-west and 

 dips south. The schist overlies it conformably. 



The Hudson River shales are faulted against the Storm King 

 granite on the north. At the south a long fault runs northeast- 

 southwest from Kent cliffs to Tompkins Cove. This is a continua- 

 tion of the fault system which makes the Ramapo mountain escarp- 

 ment to the southwest. An infaulted band of the Cambro- 

 Ordovician sediments about one-half of a mile wide follows along 

 this fault from Adams Corners on Peekskill Hollow creek to 

 Peekskill, continuing across to the west side of the river and 

 through Tonipkins Cove southwestward. 



The Cortlandt intrusives lie at the angle made by two faults or a 

 fault and a strong flexure, the continuation of Peekskill Hollow 

 fault and the Mahopac fiexture. They are distinctly unmetamor- 

 phosed and show no signs of a complicated dynamic history. 



Formations sufficiently prominent to be mapped. Several 

 easily distinguished groups of formations are represented and in 

 each group there are a certain number of readily distinguished 

 members. Tlie principal groups fall into a historical sequence, but 

 there is no intention to discuss that relation at this point further 

 than to present the general sequence from older to younger. 



The great divisions or groups of formations are: 



1 The ancient Precambrian gneisses, schists, granites and a 

 variety of related rocks. 



2 The Manhattan-Inwood-Lowerre series of crystalline schists and 

 limestones which is of questionable age. 



3 The Hudson River- Wappinger-Poughquag series of slate, lime- 

 stone and quartzite of Cambro-Ordovician age. 



4 The Cortlandt series of later intrusives. 



The relative areas represented by these four groups on the accom- 

 panying geologic map bring out the fact that group i, the ancient 

 Precambrian gneiss-schist-granite series, occupies about two-thirds 

 of the whole area and is the dominant group of this quadrangle. 



The second group, crystalline schists and limestones of doubtful 

 age, is found only in the southeast quarter of the quadrangle. 



The fourth group, the Cortlandt series, occupies a compact area 

 extending into the quadrangle from across the south line and covers 

 about 20 square miles. 



The third group, the Hudson River- Wappinger-Poughquag series, 

 is found in a triangular patch in the northwest corner of the quad- 



