GEOLOGY OF THE NEW YORK CITY AQUEDUCT 1 59 



to find rock even at 213 feet. Two others nearly a thousand feet 

 to the westward, however, found rock again at approximately the 

 same elevation as the divide. If this is a tributary stream divide 

 therefore it must have an east-west trend. 



Pagenstechers gorge 



This is a notch between Storm King ridge and Little Round top 

 occupied by a very small mountain stream. The rock floor is granite 

 gneiss of the Storm King type. Its special characters are (i) 

 extreme shattering or crushed condition, and (2) extensive decay 

 along this zone which has softened the rock constituents to great 

 depth. 



Considering the nature of the granite gneiss in general this nar- 

 row gorge is a surprisingly deep one. But this is no doubt due to 

 the influence of the decayed crush zone. The drill cores taken from 

 the holes that penetrated the floor at this place are so much altered 

 that, after several months exposure to the air, they can be readily 

 crushed in the hand. Hole no. 16/A45 which is centrally located 

 penetrated to — 196 feet. It is in material of this same condition, 

 to at least — 100 feet. Similar conditions are proven to the north 

 of the line, shown in the accompanying profile and a rapid increase 

 in depths. From the surface outcrops farther up the gulch it is easy 

 to see that the crushed zone extends in that direction with the 

 strongest lines about s. 70 w. This is doubtless on the strike of the 

 fault lines of the northern border of the range. It is of more than 

 usual interest in showing the depth to which incipient decay has 

 penetrated in these crush zones, and the efficiency of stream erosion 

 along them. 



Overthrust fault 



The principal fault line follows the margin of the granite gneisses. 

 At the best exposure of it the Hudson River slates are overridden 

 by the gneiss. This represents therefore the cutting out entirely of 

 the Wappinger limestone and the Poughquag quartzite and a part 

 of the slates by the displacement which must amount to at least 

 2000 feet and probably more. The same relation is indicated by the 

 borings and by the outcrop near the village of Cornwall, but a little 

 limestone is found midway between the two points along the strike 

 of the fault. The strike of the fault averages about n. 65° to 70° e., 

 but locally, at the best exposure, it is only n. 35° e. The dip is 

 southeast at an angle of approximately 45 degrees. 



