DETAILED STUDY OF SECTIONS 



173 



under the shoe. . . . The rock is the ordinary gneiss found on Manhattan 

 island with a dip almost vertical."* 



Russell states, on the authority of information furnished by the depart- 

 ment of docks, that the borings for foundations of the New York tower, 

 made September 10 to 23, 1877, were carried to a depth of 107.6 feet, 



i 



Figure 18.— Section across East River. 

 Along line of East River bridge number 3. 



and penetrated mica schist to a depth of 6.4 feet. He quotes Mr F. Col- 

 lingwood, chief engineer, as follows: 



" The rock on which the pier foundations rest is gneiss, with a very irregular 

 surface; in a place 172 by 100 feet the depth below high tide varied from 75 to 94 

 feet. The caisson was stopped at 78 feet." 



I 



i 



oGn. 



-1/9 





-*H-r 



I -/33 

 I 



I 

 I 



oGne/ss 



l 



l 



l 



1 



^Limestone 



l 



oG/7. 



-/O0 



\oGn 

 Gn. n 





^L 



Figure 19.— Location of Drill Holes under New York Toiver of East River Bridge Number 3. 



At the Brooklyn tower mica schist was found at a depth of 88 feet.f 

 Coentles reef. — This reef of gneiss is located in the East River channel 

 about one-third of the distance from the Battery to Joralemon street, in 



♦Reports of Executive Committee, Chief Engineer, and General Superintendent of the New 

 York Bridge Company, Brooklyn, 1872, p. 26. 

 t Russell, quoting F. Collingwood, loc. cit. 



