on that half of the roadway.  Cableways to handle the dirt were erected near the curb line, spanning a number of these trestles, and then the earth between them was excavated from the curb to within a few feet of the nearest electric car track.  The horse car tracks were removed.  Between the electric tracks a trench was dug until its bottom was level with the tops of the trestles, about three feet below the surface as a rule.  A pair of heavy steel beams was then laid in this trench on the trestles.  Between these beams and the curb line a second pair of beams were placed.  In this way the equivalent of a bridge was put up, the trestles acting as piers and the beams as girders.  The central portion of the roadway was then undermined and supported by timbering suspended from the steel beams.  The various gas and water pipes were hung from timbers at the surface of the ground.  About four sections, or 150 feet, of the subway were built at a time in this manner.  When the work was completed along one side of the street it was repeated in the same manner on the other side.  This method of construction was subsequently modified so as to permit work on both sides of the street simultaneously.  The manner in which the central part of the roadway was supported remained the same and all of the traffic was diverted to this strip.

[Illustration:  SUPPORT OF ELEVATED RAILWAY STATION AT 42D STREET AND SIXTH AVENUE]

Between 14th and 17th Streets, because of the proximity of the rock to the surface, it was necessary to move the tracks of the electric surface railway from the center of the street some twenty feet to the east curb, without interrupting traffic, which was very heavy at all times, the line being one of the main arteries of the Metropolitan system.  Four 12 x 12-inch timbers were laid upon the surface.  Standard cast-iron yokes were placed upon the timbers at the usual distance apart.  Upon this structure the regular track and slot rails were placed.  The space between the rails was floored over.  Wooden boxes were temporarily laid for the electric cables.  The usual hand holes and other accessories were built and the road operated on this timber roadbed.  The removal of the tracks was made necessary because the rock beneath them and the concrete around the yokes was so closely united as to be practically monolithic, precluding the use of explosives.  Attempts to remove the rock from under the track demonstrated that it could not be done without destroying the yokes of the surface railway.

[Illustration:  SUPPORTING ELEVATED RAILROAD BY EXTENSION GIRDER—­64TH STREET AND BROADWAY]