176 W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



Reef off Battery. — A small reef has been found recently in the North 

 river about a quarter of a mile west-southwest from pier A, with least 

 depth of 28 feet at mean low water. The rock is gneiss, as are all the 

 other reefs in the channels about New York island. 



Jersey flats. — The area of the Jersey flats to the west and southwest of 

 Ellis and Bedloes islands has been investigated through the medium 

 of borings made under the direction of the Corps of Engineers, United 

 States Army,* to determine the practicability of constructing a new chan- 

 nel in that vicinity. The rock contours and the depths to rock measured 

 from mean low water are given on figure 21. The rock encountered by 

 the drills was in all cases gneiss " nearly vertically stratified." 



For the data entered on the map of the New Jersey flats I am indebted 

 to Lieutenant Colonel C. W. Raymond, of the Corps of Engineers, United 

 States Army. Data are not available concerning the depth of bed rock 

 beneath Ellis island. For the foundation work of the new Ellis Island 

 hospital penetration tests were made, using a f-inch iron rod. On the 

 south side of Ellis island piles were driven into hard bottom at depths 

 ranging from 16 to 23 feet at mean low water. No rock was, however, 

 encountered. Buttermilk channel has been dredged to a clear depth of 

 26 feet below mean low water without uncovering rock in place. 



Hudson River tunnel from Jersey City to New York {McAdoo tunnel). — 

 The section of this tunnel (figure 22) published by Spielmann and 

 Brush f shows that a reef of rock with a steep western and a gradual 

 eastern slope rises near the east bank of the river along the line of the 

 tunnel. The highest point of this reef, along the line of the tunnel, was 

 at a depth of 89 feet below mean high water. The tunnel was first aban- 

 doned because of the difficulty of passing from the air locks to the rock, 

 but the enterprise was again taken up, and has since been successfully 

 carried through to completion as the McAdoo tunnel, of which Mr Charles 

 M. Jacobs has been the chief engineer (see figure 22). 



Projected Hudson River tunnels of the Pennsylvania Railroad Company. — 

 These tunnels, six in number, are to run from Shippen street, Wee- 

 hawken, to West Thirty-fourth street, New York. Core-drill borings 

 have been made upon the Weehawken shore, extending out to a point 

 700 feet from the Weehawken shore, from which wash borings were 

 taken at intervals of 500 feet or less to the Manhattan bulkhead line, 

 from which latter point wash and core drills were put down across the 



♦Survey of a point between Ellis island and the docks of the New Jersey Central railroad to a 

 point between Reef light and Constable hook in waters of New York bay, New Jersey. Report of 

 Major G. L. Gillespie, Corps of Engineers, United States Army, Appendix E 18. Annual report of 

 Chief of Engineers for 1882, pp. 719-724. 



tArthur Spielmann and Charles B. Brush : The Hudson River tunnel. Trans. Am. Soc. Civ. Eng., 

 vol. ix, 1880, pp. 259-277, plate viii. 



