oints that these erectors
could not be moved from working to working. The result was that about
58% of the lining was built by hand. At first thought, this seems to be
a crude and extravagant method, as the plates weighed about 1 ton each
and about 20,000 were erected by hand. As it turned out, the cost was
not greater than for those erected by machinery, taking into account the
cost of erectors and power. This, however, was largely because the hand
erection reduced the amount of work to be done by the machines so much
that the machines had an undue plant charge.

The hand erection was very simple. A portable hand-winch, with a 3/8-in.
wire rope, was set in any convenient place. The wire rope was carried to
a snatch-block fastened to the top of the iron previously built; or,
where the roof was in soft ground, the timbering furnished points of
attachment. The end of the wire rope was then hooked to a bolt hole in a
new plate, two men at the winch lifted the plate, and three or four
others swung it into approximate place, and, with the aid of bars and
drift-pins, coaxed it into position and bolted it. Where there was no
timbering above the iron, sometimes the key and adjoining plates were
set on blocking on a timber staging and then jacked up to place.

LONG ISLAND SHAFTS.

The river shafts were designed to serve both as working shafts and as
permanent openings to the tunnels, and were larger and more substantial
than would have been required for construction purposes. Plate X of Mr.
Noble's paper shows their design. They consist of two steel caissons,
each 40 by 74 ft. in plan, with walls 5 ft. thick filled with concrete.
A wall 6 ft. thick separated each shaft into two wells 29 by 30 ft.,
each directly over a tunnel. Circular openings for the tunnel, 25 ft. in
diameter, were provided in the sides of the caissons. During the sinking
these were closed by bulkheads of steel plates backed by horizontal
steel girders. The shafts were sunk as pneumatic caissons to a depth of
78 ft. below mean high water. There have been a few caissons which were
larger and were sunk deeper than these, but most large caissons have
been for foundations, such as bridge piers, and have been stopped at or
a little below the surface of the rock. The unusual feature of the
caissons for the Long Island shaft is that they were sunk 54 ft. through
rock.

It had been hoped that the rock would prove sound enough to permit
stopping the caissons at o