ded on cars at the bottom and
hoisted by derricks to cars on the disposal trestle. A locomotive was
lowered to the bottom of the excavation on August 25th, 1907, and a derrick
started operating at the bottom on August 27th, 1907. The commencement of
this work by derricks at the bottom is shown by Fig. 3, Plate LII. In
general, the disposal tracks were maintained about on the center line of
31st Street until the excavation had been carried as close to them as
possible, and on October 16th, 1907, they were shifted to the extreme north
side of the work, as shown by Fig. 2, Plate L. A portion of the old trestle
was left in place near Tenth Avenue, a derrick was erected thereon, and the
tracks were used for cars to receive the excavated material hoisted from
sub-grade. The disposal trestle was maintained in this position until such
time as it would interfere with the excavation, and then the tracks were
abandoned. This was done on November 11th, 1908. Fig. 3, Plate L, shows the
finishing of the excavation on the north side of the work. On August 30th,
1908, a cut was made under Ninth Avenue at sub-grade, and cars could then
be run from Seventh to Tenth Avenue at sub-grade. On October 24th, 1908,
the connection with the disposal trestle east of Ninth Avenue was
abandoned, and all excavated material was hoisted from sub-grade at Tenth
Avenue by derricks.

As previously stated, the contractor was required to make complete disposal
of all excavated material after January 1st, 1909, but was allowed the use
of the pier until January 20th, 1909, after which date the materials were
hoisted by derricks at Tenth Avenue, loaded on 2-horse trucks, and
transported to the 30th Street pier, North River, where it was loaded on
scows by two electric derricks. A considerable amount of the rock
excavation was broken up and used for back-fill.

_Earth Excavation._--Practically all the earth excavation, amounting to
about 57,000 cu, yd., was done with steam shovels. The average quantity of
earth excavated by a steam shovel per 10-hour shift was 180 cu. yd. This
material was loaded on side-dump cars and taken to the disposal pier where
it was dumped through chutes to the decks of scows. Inasmuch as the
quantity of earth excavation was small, as compared with the rock, the
earth was used principally for the first layer on the scows for padding, so
that small stones might be dumped through the chutes without injuring the
decks.

_Rock Excavation.