﻿1 88 NEW YORK STATE MUSEUM 



Under the conditions of work, this is a fair saving and indicates 

 much more substantial rock below the -75' level. There are many 

 pieces 10-12 inches in length and for a 1 inch core this may be 

 considered very good. 



It is clear, however, from a detailed inspection of the cores, that 

 there is considerable variation somewhat independent of depth. 

 There are occasional stretches of poorer ground in the midst of 

 comparatively sound rock. This is believed to indicate that the 

 crushed condition is confined chiefly to certain zones, and that these 

 zones dip across the formation and across the holes at an angle. 

 They are probably distributed promiscuously throughout the central 

 portion of the valley, but are certainly more abundant and more 

 strongly marked in the vicinity of hole no. 2 than at any other point 

 tested. The rock profile shows that hole no. 2 has also the lowest 

 bed rock. This is a further support to the general explanation of 

 the valley as given above. 



The chief elements of uncertainty remaining after the borings 

 have been completed are : 



1 The exact extent or widths of the chief crush zones 



2 Their dip and strike 



3, The possibility of others not yet touched 



4 The permeability of the rock for underground water 



5 The supporting strength of such rock in a tunnel of large 

 dimensions 



In spite of the uncertainties enumerated, the conditions are 

 entirely understandable. There is little probability of finding a 

 worse condition than that shown in hole no. 2. The permeability or 

 porosity of these zones is of course unknown. The chief reason for 

 believing that underground circulation is not abnormally heavy is 

 the observation that the joints are well filled with chlorite and that 

 other decay is not at all prominent at the lower levels. Further- 

 more, the rock is a crystalline type of rather successful resistance 

 to ordinary solution agencies and therefore may be depended upon 

 to hold its own in its present condition indefinitely. But because 

 of the poor binding effect of the chlorite it is to be expected that 

 blocks will fall from the roof of any tunnel where it passes through 

 a crush zone. Timbering will be required for protection in places, 

 but the ground will not cave or run. These zones may be expected 

 throughout a total distance of about 700 feet — i. e. the space 

 between no. 1 and no. 15. The chief belt of such ground probably 

 lies between holes no. 2 and no. 5. 



