be supported during construction. A temporary wooden bent was used to
carry the elevated structure. The elevated columns were removed until
the subway structure was completed at that point. (See photograph on
page 45.)

[Illustration: SMALL WATER MAINS BETWEEN STREET SURFACE AND SUBWAY
ROOF, SUBSTITUTED FOR ONE LARGE MAIN--125TH STREET AND LENOX AVE.]

[Illustration: SPECIAL CONSTRUCTION OF 6-1/2-FOOT SEWER, UNDER CHATHAM
SQUARE]

A feature of the construction which attracted considerable public
attention while it was in progress, was the underpinning of a part of
the Columbus Monument near the southwest entrance to Central Park.
This handsome memorial column has a stone shaft rising about 75 feet
above the street level and weighs about 700 tons. The rubble masonry
foundation is 45 feet square and rests on a 2-foot course of concrete.
The subway passes under its east side within 3 feet of its center,
thus cutting out about three-tenths of the original support. At this
place the footing was on dry sand of considerable depth, but on the
other side of the monument rock rose within 3 feet of the surface. The
steep slope of the rock surface toward the subway necessitated
particular care in underpinning the footings. The work was done by
first driving a tunnel 6 feet wide and 7 feet high under the monument
just outside the wall line of the subway. The tunnel was given a
2-foot bottom of concrete as a support for a row of wood posts a foot
square, which were put in every 5 feet to carry the footing above.
When these posts were securely wedged in place the tunnel was filled
with rubble masonry. This wall was strong enough to carry the weight
of the portion of the monument over the subway, but the monument had