At the station on 42d Street, between Park and Madison Avenues, where there are five subway tracks, and along 42d Street to Broadway, a special method of construction was employed which was not followed elsewhere. The excavation here was about 35 feet deep and extended 10 to 15 feet into rock. A trench 30 feet wide was first sunk on the south side of the street and the subway built in it for a width of two tracks. Then, at intervals of 50 feet, tunnels were driven toward the north side of the street. Their tops were about 4 feet above the roof of the subway and their bottoms were on the roof. When they had been driven just beyond the line of the fourth track, their ends were connected by a tunnel parallel with the axis of the subway. The rock in the bottom of all these tunnels was then excavated to its final depth. In the small tunnel parallel with the subway axis, a bed of concrete was placed and the third row of steel columns was erected ready to carry the steel and concrete roof. When this work was completed, the earth between the traverse tunnels was excavated, the material above being supported on poling boards and struts. The roof of the subway was then extended sidewise over the rock below from the second to the third row of columns, and it was not until the roof was finished that the rock beneath was excavated. In this way the subway was finished for a width of four tracks. For the fifth track the earth was removed by tunneling to the limits of the subway, and then the rock below was blasted out. [Illustration: MOVING WEST SIDE WALL TO WIDEN SUBWAY FOR THIRD TRACK--135TH STREET AND BROADWAY] [Illustration: SUBWAY THROUGH NEW "TIMES" BUILDING, SHOWING INDEPENDENT CONSTRUCTION--THE WORKMEN STAND ON FLOOR GIRDERS OF SUBWAY] [Illustration: COLUMNS OF HOTEL BELMONT, PASSING THROUGH SUBWAY AT 42D STREET AND PARK AVENUE] In a number of places it was necessary to underpin the columns of the elevated railways, and a variety of methods were adopted for the work. A typical example of the difficulties involved was afforded at the Manhattan Railway Elevated Station at Sixth Avenue and 42d Street. The stairways of this station were directly over the open excavation for the subway in the latter thoroughfare and were used by a large number of people. The work was done in the same manner at each of the four corners. Two narrow pits about 40 feet apart, were first sunk and their bottoms covered with concrete at the elevation of the floor of the subway. A trestle was built in each pit, and on these were placed a pair of 3-foot plate girders, one on each side of the elevated column, which was midway between the trestles. The column was then riveted to the girders and was thus held independent of its original foundations. Other pits were then sunk under the stairway and trestles built in them to support it. When this work was completed it was possible to carry out the remaining excavation without interfering with the elevated railway traffic.