GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK II3 



lands. It appears also that the marine waters deepened and condi- 

 tions of deposition changed to such a degree that a thousand feet 

 of limestone was deposited, representing the Wappinger. Certain 

 beds of this series carry marine fossils. Whether there is a break 

 anywhere in the series does not appear in the rocks in this quad- 

 rangle, but whatever there may be is not a real unconformity be- 

 cause in all essential respects the series is conformable and con- 

 tinuous. Above the limestone an immense thickness of slates, 

 graywackes and sandstones were developed which is known 

 in this district as the Hudson River formation. The source of this 

 material was undoubtedly some earlier series of somewhat metamor- 

 phosed sediments as already indicated. The deposition of this mem- 

 ber, whose thickness is not known, must represent a shallowing of 

 the sea and perhaps even occasional delta deposit conditions, but 

 marine fossils are found in certain layers to the north and the struc- 

 tural behavior of the rock as a whole would lead one to suppose it 

 to have been deposited under water and with good sorting. 



Post-Ordovician revolution or deformation. At the close of the 

 Cambro-Ordovician deposition the region was subjected to elevation 

 and to the deformation of the Taconic epoch. Such a step would not 

 be determinalble, as a separate item, from the structural features of 

 this quadrangle, but doubtless a part of the deformation which might 

 otherwise be credited to the Appalachian stage belongs here. It is 

 probable that the deformation of Taconic time has furnished, through 

 subsequent erosion, the new supplies of sediments of mixed type 

 for the great series of formations constituting the rest of the 

 Paleozoic series. The Devonian bluestones and shales show chiefly 

 lithic grains derived from some older somewhat metamorphosed 

 formation, just as the Hudson River formation did before them. 

 The fact that such grains were available indicates that these earlier 

 formations, probably including the Hudson River, were enough 

 metamorphosed at that time to furnish these grains of slates and 

 phyllites and graywackes of which the Devonian beds are in large 

 part composed. 



Post-Ordovician erosion. Definite traces of this interval which 

 is well marked a few miles farther north, are not determinable in 

 this area. The best evidence of its existence are the qualities of 

 material furnished to the succeeding formations as indicated in the 

 paragraph above. It is entirely possible and indeed probable that 

 great thicknesses of middle and later Paleozoic strata were formed 

 on some of this ground. Many hundreds of feet of Devonian sedi- 



