162 W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



with the faults believed to have occurred in the western gorge of the 

 Harlem river. If they there exist, Fordham heights would appear to be 

 a long " horst " or " briicke " lying between parallel faults and agreeing 

 closely, both in size and orientation, with the u horst" of Washington 

 heights, a little farther west. 



One hundred and forty-fifth Street bridge. — This bridge has five piers? 

 four of which rest on white marble and the fifth on " extreme hard-pan. "* 

 Crystalline limestone is also exposed at the surface near the New York 

 end of the bridge. The section along this bridge reproduced in figure 7, 

 like that at certain other bridges, affords no evidence that the river here 

 flows in a rock gorge. 



t-f/t/inq 



WSancf 



Sand end Gravel \ . . 

 JJu^yet and Boulders : 



Figure 7. -Section across the Harlem River. 

 Along line of One hundred and forty-fifth Street bridge. 



Rapid Transit tunnel. — This tunnel connects Lenox avenue and One 

 hundred and forty-first street, on Manhattan, with Westchester avenue, 

 in the Bronx. The approximate surface of the rock in the vicinity of 

 Harlem river along the line of this tunnel is brought out in the profile 

 of figure 8. The rock penetrated is limestone.f 



Madison Avenue bridge, Harlem river. — This bridge rests on piles, which 

 at no point reach to bed rock.J Russell gives the data for a section 

 across the river at this point.§ 



* Information furnished by Mr F. W. Allen, engineer for the contractor, who also kindly sup- 

 plied data for the section. 



t Information and profile furnished by Mr George S. Rice, deputy chief engineer, Rapid Transit 

 Railroad commissioners. 



J Information furnished by Mr A. P. Boiler, consulting engineer, and Mr McLean, engineer of 

 the comptroller's office. 



g I. C Russell ; Geology of Hudson county, New Jersey. Ann. N. Y. Acad. Sci., vol. ii, 1882, p. 75. 



