164 W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



Willis Avenue bridge. — About 200 feet out from the Manhattan shore 

 the center pier of this bridge, at a depth of 80 feet below mean high 

 water, rests in part on a ledge of marble and partly on boulders. The 

 other piers rest on boulders (see figure 12). Mr E. A. Byrne, assistant 

 city engineer, has preserved a sample of the marble, which was submitted 

 to the writer for examination. It is a white coarsely crystalline rock 

 like that quarried at Tuckahoe. 



NEW YORK SIDE(SW) 



Figure 9. — Section across Harlem River at Park {Fourth) Avenue. 



One hundred and twenty-fifth and one hundred and twenty-second Street 

 reefs, East river. — The first mentioned of these is in the mid-channel of 

 the East river off One hundred and twenty-fifth street, and the second 

 about 300 feet off the foot of One hundred and twenty-second street. 

 Both reefs are of gneiss and have been reduced in height by the Corps 

 of Engineers, United States Army.* 



South Rest Pier 

 North 



I I/O' 



Gneiss > 



-.■so'—fii/oor of Caisson 

 Rock ' 



South 



100 



Figure 10.— Section across Harlem River. 

 Along line of Third Avenue bridge. 



Projected Hell Gate railroad bridge. — The New York Connecting Rail- 

 road Company, of which Mr A. P. Boiler, is chief engineer, has pro- 

 jected a double-track railroad bridge across the East river at Hell Gate 



♦Report of the Chief of Engineers, United States Army, 1896, part i, p. 106. The writer is in- 

 debted to Captain Edgar Jadwin, Corps of Engineers, United States Army, for information regard- 

 ing the composition of these reefs. 



