174 



W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



■U-- 



Brooklyn. It is therefore quite near the line 

 of the Whitehall Street tunnel, now being 

 constructed. 



Rapid Transit tunnel \under East river. — 

 The course of this tunnel is from the foot 

 of Whitehall street, Manhattan, to the foot 

 of Joralemon street, Brooklyn. The data 

 from the preliminary wash and core drill 

 borings for this tunnel are set forth in fig- 

 ure 20, which is reproduced from supple- 

 mentary drawing 2-D-24 of the Rapid 

 Transit Railroad commissioners. On au- 

 thority of Mr George S. Rice, deputy chief 

 engineer for the commissioners, the rock of 

 all the cores is gneiss, no limestone being 

 anywhere found in the section. The section 

 is nearly complete across the river, there 

 being, however, two deep channels separated 

 by a sharp reef about a quarter of a mile 

 from the Brooklyn shore, the bottom of 

 which was not found by the drills at the 

 depth of about 100 feet. The quite remark- 

 able and abrupt changes of level shown by 

 the surface of bed rock is in all respects of 

 the type revealed by the borings^of the same 

 commission along the line of Broadway be- 

 tween the Battery and Union square. 



Deep well on north shore of Governors island. — 

 This well entered the rock at a depth of 69 

 feet 10 inches. It had, when last reported 

 to the writer, been carried to a depth a little 

 in excess of 1,800 feet, and had penetrated a 

 micaceous type of gneiss for the entire dis- 

 tance.* The same type of rock is said to 

 occur on the south shore of the island. 



Diamond reef. — This obstruction to naviga- 

 tion, which is now being removed, is located in 

 mid-channel a little north of Governors island 

 in the direction of Coenties reef. Like the 

 latter, it consists of the common type of gneiss. 



information furnished by John Sampson, chief quartermaster, Governors island, 



New York. 



