152 W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



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Tunnels of the Pennsylvania Railroad Company 170 



Twenty-sixth Street and Third Street reefs 171 



East River bridge number 2 (Williamsburg bridge) 171 



East River bridge number 3 171 



Brooklyn bridge 172 



Coenties reef 173 



Rapid Transit tunnel under East river 174 



Deep well on north shore of Governors island 174 



Diamond reef. 174 



Reef off Battery 176 



Jersey flats . 176 



Hudson River tunnel from Jersey City to New York (McAdoo tun- 

 nel) 176 



Projected Hudson River tunnels of the Pennsylvania Railroad Com- 

 pany 176 



Proposed New York and New Jersey bridge 178 



Conclusions respecting the origin of the channels 179' 



Harlem river 179 



East river 180 



Hudson river 180 



Former hydrography of Manhattan island 181 



Introduction 



The engineering work recently completed and that now undertaken 

 in and about the city of New York make it easily the focus for such 

 enterprises on the planet — enterprises the cost of which must be esti- 

 mated in the hundreds of millions. To mention but a few, there are the 

 subway and the tunnels of the Rapid Transit railway, the East River 

 bridges numbers 2, 3, and 4, the proposed tunnels of the Pennsylvania 

 Railroad Company from Weehawken to Long Island City beneath the 

 two rivers and Manhattan island, "the completion of the old Hudson 

 River tunnel from Jersey City to New York, and the dredging of the 

 Buttermilk and Ambrose channels and of the Man-o'-War and Diamond 

 reef3 by the United States government. These are some of the larger of 

 the recent enterprises. Of earlier ones, the government work in making 

 the channel of Hell Gate by removing Flood and Mill rocks, the con- 

 struction of the Croton and the new New York aqueducts, Dyckmans 

 cut in the ship canal at Kings bridge, the East River Gas Company's 

 tunnel from New York to Long Island City beneath Blackwells island, 

 and the numerous bridges spanning the Harlem river, have all facilitated 

 the work of the geologist within the New York city area. Taken to- 

 gether, they have furnished more than 35 sections crossing the rivers 

 forming the water front of the island, many of them revealing the nature 



