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NEW YORK STATE MUSEUM 



fact that there was an artesian flow from this hole of 10 gallons per 

 minute after reaching a depth of 80 feet, which increased to 15 

 gallons per minute after reaching a depth of 253 feet. This under- 

 ground supply is maintained since completion and the pressure is 

 sufficient to raise the water about 15 feet above the surface. 



This is a behavior that is consistent with the geologic conditions. 

 The boring has no doubt penetrated a crush zone following one of 

 the faults which enters this side of the valley. The crush zone dips 

 steeply and the boring has penetrated the hanging wall of more 

 solid rock in the first 50 feet and, after reaching the broken and 

 decayed portion of the zone, has swung off parallel to the dip and 

 avoiding the more resistant foot wall has followed down on the soft 

 inner streak. 



;, Def/ecfionof cjrijj 



Fig. 30 Sketch illustrating the interpretation of geologic structure across Foundry- 

 brook valley indicating the relation of certain borings to them and their supposed 

 influence in deflecting the drills 



This crush zone extends on northeastward across higher ground 

 where opportunity for taking in surface water is offered. This is 

 without doubt the source of supply for the circulation which fur- 

 nishes the artesian flow and which has been so effective in pro- 

 ducing decay to great depth. But the circulation and associated 

 decay are probably limited to comparatively narrow zones. There 

 is no good reason for assuming large masses of rotten gneiss at 

 great depth. The worst zones are narrow but may be comparatively 

 deep, i. e. they may extend much deeper than any of the borings yet 

 made in this valley. The depth of decay is related to the outlet for 

 underground circulation which in this case is the gorge of the 

 Hudson. 



