d bench. Part of the muck handled
by hand and part by steam shovel.

Exploration drift about 10 ft. by 13 in. Muck loaded by
hand. 14 ft. timbered.

At portal of twin tunnels. Drift excavated to full
width and bench. Muck loaded by hand. 12 ft.
timbered.

Drift excavated to full width and bench. Muck loaded
by steam shovel. Full-width tunnel timbered for 26
ft. independently of the main excavation.
=======================================================

THREE-TRACK TUNNEL EXCAVATION.

When it became evident that the work through the Fifth Avenue section
would be extremely slow, shafts were sunk in each street between Sixth
and Seventh Avenues. The shafts, as shown on Plate XIV, were located in
the streets, but in such a way as to block only half of the roadway. At
the same time it was decided to construct in open cut about 200 ft. of
the Three-Track Tunnel at the west end of the contract in 32d Street,
where the rock surface was below the top of the tunnel. It was hoped
that the remainder of the work could be built without opening the
street, but further investigation showed that this was impracticable,
and eventually all the Three-Track Tunnel in 32d Street, except 120 ft.
east of the shaft, was built in open cut.

_Thirty-second Street Work in Tunnel._--Following the sinking of the
shaft, a drift was driven across the street at the crown of the tunnel,
and a top heading on the south side was excavated in both directions.
Frequent cross-drifts to the north side showed that the rock was nowhere
very sound and that, except for a short distance east of the shaft, it
was distinctly unfavorable for the wide Three-Track excavation. In this
stretch the north ends of these cross-cuts were connected by a second
heading, and wall-plates and sets of three-segment arch timbering were
set up to support the roof of the drifts. The cross-cuttings were
gradually widened and timbered until the entire excavation had been made
down to the level of the wall-plates, as shown in Fig. 3, Plate LX. The
bench was then excavated in two lifts, leaving the wall-plates supported
on narrow longitudinal berms, which were removed in short sections to
permit the placing of posts under the wall-plates.

_Thirty-second Street Open-Cut Work._--Before actual open-cut excavation
was started, all buildings facing it were underpinned to rock. For this
purpose, a trench was dug along the face of the buildings and of the
same depth as