een set and braced, an 8-in. brick wall was laid
up the face of the rock, containing a vertical line of three-cell hollow
tile block every 5 ft. of length, and laid to conform as nearly as
possible to the face of the rock, all voids being filled with broken
stone. Water-proofing, similar to that described for the walls in the
trench, was then applied to the brick and tile wall for the full height,
and firmly braced to the front forms, the braces being removed as the
concrete reached them. The concrete was mixed at the street level and
deposited through chutes, as described previously.

Tables 1, 2, and 3 show the quantity of cement used in each section of
retaining wall, and give figures by which the quantities of other
materials may be determined.

_Pit Excavation._--The pit excavation during the horse-and-truck period
was largely preparatory work done to get the excavation in good shape
for handling spoil trains after Pier No. 72 and the trestle approach
were finished. This required an open cut from Ninth to Seventh Avenues
at a sufficient depth below the sewers and other substructures in the
avenues to clear a locomotive, and wide enough for both running and
loading tracks, also the building of the cast-iron sewer in Eighth
Avenue across the entire excavation, with enough of the temporary
bridging to support it. The building of the trestle in Eighth Avenue
was essentially a part of the pit excavation, as the progress of one
depended greatly on that of the other.

Excavation was commenced on July 12th, 1904, for the crossing under
Ninth Avenue, and in the pit east of Ninth Avenue along 32d Street. The
line chosen for the opening cut was down the center of the pit, as it
was not safe to excavate near the bounding streets until after the
completion of the enclosing retaining wall. The excavation was started
by hand, but three 70-ton Bucyrus steam shovels were put to work as soon
as they could be delivered, the first on July 25th and the third on
September 12th. The excavated material was loaded by the shovels on
end-dump wagons, each having a capacity of 2 cu. yd., and was conveyed
in them to the dumping board at 35th Street. The average number of teams
was 135, 10% being snatch teams to pull the wagons out of the pit and to
assist them up the runway at the dumping board. The teams averaged only
seven trips per day of 10 hours, considerable delay being caused by the
trains of the New York Central Railroad at Eleventh