girders. Nov. 14, 08.]

[Illustration: PLATE XLVIII, FIG. 4.--TW 58, P.T. & T.R.R. Co. Terminal
Station West. East side of Ninth Ave. looking North from 31st St., showing
underpinning of Ninth Ave. Structures. Aug. 10, 08.]

Fig. 4, Plate XLVII, and Fig. 1, Plate XLVIII, show the structures
supported on the central rock core and the excavation on the east side to
permit of the erection of the permanent viaduct girders. Fig. 1, Plate
XLVIII, shows also the easterly portion of the concrete north abutment.
Fig. 2, Plate XLVIII, shows five rows of the permanent viaduct girders
erected on the east side of the work.

The excavation of the sides of the avenue having been completed, and six
rows of permanent viaduct girders erected on both sides, timber bents, as
shown on Figs. 2, 4, 5, and 6, were erected on this steel to support the
ends of the girders "C" and carry the structure while the rock core was
being excavated. Fig. 3, Plate XLVIII, shows the method of taking the
weight on these bents. Four 80-ton jacks were used, and oak blocks were
placed on the top of each jack to transmit pressure to a temporary oak cap
under the girders "C" independent of the bents; all four of these jacks
were operated simultaneously, and the girders "C" were lifted off the bents
and clear of the concrete piers. Oak filling pieces were then inserted
between the bents and the girders "C," so that when the jacks were released
the girders "C" were clear of the concrete piers. Fig. 3, Plate XLVIII,
shows that the girders have been lifted off the piers. Elevations were
taken on each set of girders during each operation, and careful
observations were made on the elevated railway columns. Where the rock was
very close to these bents, the open space between the posts was filled with
blocking so that there would be less danger of the bent shifting if struck