DETAILED STUDY OF SECTIONS 167 



ural planes of the rock penetrated by the tunnel. Much attention has 

 been given to the rock composition by the engineers who have written on 

 this tunnel, and their descriptions have been supplemented by the petro- 

 graphic studies of Professor Kemp. For the greater part of the distance 

 the rock is a gneiss of varying hardness, in this respect reaching a maxi- 

 mum in the hornblende gneiss encountered under the east side of Black- 

 wells island. Under the bottom of the west channel a considerable 

 thickness of soft decomposed rock was found, which Kemp has shown to 

 be, in part at least, the residue from the alteration of one large and a 

 number of smaller pegmatite veins. Beneath the east channel a thick- 

 ness of about 350 feet of hard white marble was found enclosed between 

 soft decomposed bands, which appear to correspond to nearly vertical 

 fissure planes. The loose material filling these zones about the fissures 

 is in part decomposed pegmatite and in part altered mica schist. In a 

 personal letter Mr Davies has added some valuable notes concerning the 

 nature and direction of the fissures both in the east and the west chan- 

 nels. He says : 



"Under the New York end of the tunnel is highly micaceous gneiss rock. Just 

 outside of the pier line it intersected a fissure. . . . Under the east channel 

 is a seam of about 350 feet of dolomite, bounded on both sides by fissures of com- 

 pletely decomposed (and soapstone-like) mica schists. . . . The dip of these 

 fissure faces is about 22 degrees off the vertical.* The strike is slightly west of 

 north. 



" Curiously, when we were excavating the foundations for the Rainey bridge, 

 which was to be built at Sixty-fourth street, New York, we found at the site of 

 the pier on the west side of Black wells island a fissure exactly corresponding in 

 the direction and strike to the one tunneled through opposite Seventieth street. 

 In this last case, however, although it appeared 15 feet wide at the top surface of 

 rock (some 10 feet below mean low water), we excavated it entirely out to a sharp 

 V, at a depth to the point of the V about 25 to 30 feet below mean low water." 



Fissures found along the line of this tunnel seem, therefore, to be in- 

 cluded in a parallel series, the strike of which is a few degrees west of 

 north and the hade of which varies from 78 degrees east to a very steep 

 angle west. One of the faults discovered under the pier of the Rainey 

 bridge belongs to a different series following the course of the channels 

 in this vicinity. 



Projected but abandoned Rainey bridge. — The location of this bridge 

 was to have been from the north side of Sixty-fourth street, in Manhat- 

 tan, to the foot of what is named on the maps Harsell street, Long 

 Island City, though as a matter of fact no such street exists. The work 



♦This appears to refer to the fissures in the western channel only, for the sections of Aims and 

 Jacobs show that those of the east channel are quite close to the vertical.— Ed. 



XXIII— Buia. Geol. Soc. Am., Vol. 16, 1904 



