GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK I3I 



The next member below in each case is a hmestone, varying from 

 600 or 700 feet to more than looo feet, the larger figure represent- 

 ing the Wappinger of the northern series and the smaller figure 

 representing the Inwood of the southern series. 



Beneath the limestone of the northern series is always a quartzite 

 with a thickness of approximately 600 feet. Beneath the limestone 

 of the southern series there is in some places a quartzite of very 

 moderate thickness, not over lOO or 200 feet at a maximum, but this 

 quartzite member is usually lacking. It is seen, therefore, that the 

 two series are similar in succession and somewhat also in quality 

 barring a great discrepancy in amount of metamorphism. In original 

 condition they must have been strikingly similar. 



2 In both cases the formation beneath the whole series is a com- 

 plex of gneisses and granites, and in most places the exact relation 

 to this underlying gneissic series is obscure. 



3 Both series have been very much modified by deformation, so 

 that the members are folded and sheared, and faulted in a very 

 complex manner. 



4 It is frequently stated that the sedimentary formations can be 

 followed through the Highlands in New York, clearly connecting 

 the two sides and proving them to be one formation. On the basis 

 of such a statement workers in adjacent districts have assumed an 

 identity of the two series which is not necessarily proved. As a 

 matter of fact the nearest approach of the two series to each other 

 is in the Peekskill valley and the adjacent ground just to the east, 

 and even here the structural relations are so obscure that such a 

 statement as this needs to be regarded with considerable caution. 



5 Description of the variations in the Hudson River series north 

 of the Highlands indicates that to the eastward, from the Hudson 

 river toward the Green mountains or toward the Massachusetts line, 

 the formation becomes gradually more and more crystalline until it 

 exhibits all the petrographic complexity and peculiarity of the typical 

 Manhattan schists of the south. This strikingly crystalline condi- 

 tion, in what is admitted to be the Hudson River series, removes one 

 of the fundamental objections to its identity with the Manhattan. 

 This objection is that along the Hudson river the wide difference of 

 appearance is a strong support to actual difference in age. The 

 crystalline behavior on the north side, however, toward the east, is 

 not necessarily a proof of their identity because it may be conceived 

 that the Hudson River formation, which is of similar original com- 

 position to the Manhattan, would become, under metamorphism, a 

 rock of very like petrographic habit whether of the same age or not. 



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