from the surface down. On the east side of the street, however, at the
surface was sand, which extended 15 feet down to a sloping rock
surface. The tendency of the sand to a slide off into the rock
excavation required great care. The work was done, however, without
interference with the street traffic, which is particularly heavy at
that point.

[Illustration: DUCTS IN SIDE WALLS--EIGHT ONLY OF THE SIXTEEN LAYERS
ARE SHOWN]

[Illustration: REINFORCED CONCRETE CONSTRUCTION]

[Illustration: ROOF SHOWING CONCRETE-STEEL CONSTRUCTION--LENOX AVENUE
AND 140TH-141ST STREETS]

[Illustration: SECTION OF SUBWAY AT PEARL STREET
This construction was made necessary by encountering a layer of Peat
resting on Clay]

[Illustration: SURFACE RAILWAY TRACKS SUPPORTED OVER EXCAVATION ON
UPPER BROADWAY]

[Illustration: SUBDIVISION OF 36" AND 30" GAS MAINS OVER ROOF OF
SUBWAY--66TH STREET AND BROADWAY]

The natural difficulties of the route were increased by the network of
sewers, water and gas mains, steam pipes, pneumatic tubes, electric
conduits and their accessories, which filled the streets; and by the
surface railways and their conduits. In some places the columns of the
elevated railway had to be shored up temporarily, and in other places