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NEW YORK STATE MUSEUM 



there is no doubt that an advantage will be gained both in the 

 greater imperviousness of the rock and the greater case of pene- 

 tration. Wherever the conglomerate is undisturbed it is perfectly 

 good, but where broken the crevices are but imperfectly healed 

 and circulation is unhindered. It would therefore be desirable to 

 know whether at — 250 feet the whole of the downward wedge of 

 Shawangunk could be avoided. The borings indicate a thickness 

 of Shawangunk of 345 feet in hole no. 11 where it is cut at a 

 small angle, and a thickness of 409 feet in hole no. 36 where it prob- 

 ably lies pretty flat. This greater thickness together with the 



Fig. 21 Structural geologic detail of the Coxing kill section 



finding of crushed rock at about the — 100 foot level leads to the 

 conclusion that the formation is overthickened here by the thrust 

 fault to the extent probably of about 75 feet. The true thick- 

 ness of the formation at this point is doubtless more nearly 300 

 feet than either of the figures obtained directly from the two 

 holes. If this interpretation is used as the basis of plotting a 

 cross section [see accompanying cross section] it is apparent that 

 the conglomerate should not be expected to extend more than a 

 few hundred feet east of hole no. 36 and it probably does not reach 

 a much greater depth than the — 236 feet represented as its base 

 in that boring. 1 



1 Construction of the tunnel has progressed far enough through this sec- 

 tion to prove that the Shawangunk formation does not reach much lower. 

 It forms the roof of the tunnel for some considerable distance but does not 

 come down into the tunnel more than a foot or two. 



