From a point north of 157th Street and Broadway almost to Dyckman Street, that is, a distance of nearly two miles, the New York Subway passes under an elevation known as Fort Washington Heights, which almost bounds Manhattan Island at its upper end near the Harlem Ship Canal. Under this elevation the rapid transit railroad was constructed in tunnel. The tunnel was driven from two intermediate shafts over 110 ft. deep, located one at 169th Street and the other at 181st Street and Broadway. Both shafts were sunk at one side of the center line of the tunnel. After these shafts had been utilized for working purposes during the construction of the tunnel, they were equipped with electric elevators to carry passengers from the streets to the deep station. [10] Condensed from a paper by Stephen W. Hopkins in _Harvard Engineering Journal_, April, ’08. =Material.=--The material encountered in the excavation of the Fort George tunnel was the usual mica schist met everywhere on Manhattan Island. It was full of seams with strata running in every direction to such an extent that at many points the roof of the tunnel had to be supported by timbers; at other parts along the line the rock was so disintegrated that it was considered a very loose and treacherous soil. Two serious accidents, each accompanied by loss of life, occurred during the construction of this tunnel. Both of them were caused by the sudden fall of a large ledge of rock which, after the tunnel had been excavated to the full section, remained hanging on the roof, deprived of any support and held in place by the little cohesion of the material packing the seams.