GEOLOGY OF THE WEST POINT QUADRx\NGLE, NEW YORK 97 



It is Still uncertain, however, just what depth the preglacial gorge 

 has. The boring from the river surface had reached only 765 feet 

 and the borings from the side shafts had tested solid rock at 950 feet. 

 The old channel bottom therefore lies somewhere between, but at 

 just what point there is no possibility of knowing. 



Assuming, therefore, that there might not be much of a thickness 

 of rock above the 950 foot point reached by the shallower oblique 

 borings, the engineers in charge of the project decided to locate the 

 tunnel at a depth of 11 00 feet so that there would be more than 

 250 feet of solid rock above the roof of the tunnel. This is the 

 way it was constructed. 



Two dangers were faced in constructing a tunnel of this kind, first, 

 that crevices or broken ground would be encountered, furnishing 

 extraordinary amounts of water, which might interfere seriously 

 with construction; second, that in operation the bursting pressure 

 from the water flowing inside might rupture the tunnel and establish 

 objectionable leakage. There was possibility also of encountering 

 ground difficult to grout and seal against leakage, if not kept within 

 properly protected formations. As a matter of fact, the fear of 

 heavy inflow of water was a very live one, and extra precautions 

 were taken in that direction, a considerable plant being established 

 for pumping purposes. No serious difficulties, however, were 

 encountered in this direction except temporarily when a water-bear- 

 ing seam was cut, which flooded the east shaft beyond the capacity of 

 the pumps then in operation. Later, additions to the pumping 

 equipment were made on a large scale as a guard against emergencies 

 but no further difficulties were encountered. 



The tunnel is finished with a solid concrete lining inside the 

 granite walls averaging nearly 2 feet thick, and the joints in the rock 

 back of it are filled with grout which was forced into them under 

 pressure. The inside surface in contact with the water is smooth 

 and the finished tunnel is 16 feet in diameter. The aqueduct waters 

 thus pass down on the west side of the river to iioo feet below sea 

 level and up again on the east side, rising by steps in Breakneck 

 mountain on the east to an elevation of about 400 feet above the 

 river and at this level a tunnel passes through Brealcneck mountain. 

 The aqueduct then crosses the adjacent valley on the east side and 

 thence through Bull hill on its v/ay toward New York City, finally 

 leaving the quadrangle a few miles east of Peekskill. 



The Popping rock of Storm King. A more serious matter was 

 presented by the strained condition of the granite encountered in 



