GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK ^J 



actually missing at the fault line. The Breakneck fault is a great 

 thrust, causing the gneisses and granite of Storm King and Break- 

 neck ridge to ride up on the Hudson River slates. The Tompkins 

 Cove-Peekskill Valley fault is connected with a down-dropped block 

 and must have a different structural relation and movement. Since 

 these two are characteristic of the faulting of the region they deserve 

 a special descriptive note. 



The Storm King-Breakneck fault. This fault is readily traced 

 by the abrupt change in formations in the northwest corner of the 

 quadrangle, but the ground is badly covered in most of this area and 

 the actual condition is very much obscured. Immediately to the 

 southwest, however, just beyond the margin of the quadrangle on the 

 north side of Storm King mountain the fault is well exposed and 

 very definitely located both on the surface and several hundred feet 

 beneath in the Catskill aqueduct tunnel (Moodna tunnel). The 

 fault plane is simple, and is traceable in fairly definite form for a 

 considerable distance. It dips at not far from 45 degrees to the 

 southeast. 



The rock in the hanging wall is the Storm King granite and 

 gneiss, chiefly the mixed types that are called gneisses, rather than 

 the Storm King granite proper. The foot wall is at some places 

 Hudson River slate and at other places Wappinger limestone. In 

 the vicinity of the Catskill aqueduct line, the surface shows slates 

 and the tunnel level 300 feet lower shows limestone. In both cases 

 the adjacent rock is crushed on an immense scale, especially on the 

 foot wall side. For 200 feet the limestone cut by the aqueduct tun- 

 nel in the foot wall is crushed and rehealed to such degree that it is 

 absolutely impossible to determine the bedding of the rock. Its 

 exact attitude therefore is entirely unknown. In addition, blocks 

 of slate are dragged into the principal fault zone and some of the 

 gneisses are so crushed and altered as very nearly to resemble the 

 slate. 



It is perfectly clear that this is a thrust fault, that the Highlands 

 gneisses and granite have been pushed over the bordering quartzite- 

 limestone-slate series and that the movement has been sufficient to 

 cut out all the quartzite and at most points all the limestone. Prob- 

 ably such patches of limestone as are found are dragged into place 

 by the fault movement. Since the quartzite is rather continuously 

 about 600 feet in thickness in this district and the limestone is more 



