while trains were passing over it, and occasionally trains were stopped
during a heavy or uncertain blast. A watchman on the surface, day and
night, and at first one and later two flagmen on the elevated railway
structure, were on duty at all times, reporting to the Interborough Rapid
Transit Company, by whom they were employed. Log mats and timber protection
for the girders and the columns of the permanent viaduct were used, as
shown by Figs. 1 and 4, Plate XLIX, during the excavation of the rock core,
and timber was also used to protect the face of the completed portions of
the concrete abutments.

In excavating the sides of the avenue, the rock broke better on the east
than on the west side, where large seams developed and some slides
occurred.

_Abutments._--As shown on Fig. 7, the face of the north abutment has a
batter of 2 in. to the foot, and the face of the south abutment has a
variable batter, the base being on a grade and the bridge seat being level,
and both maintaining a uniform distance from the center of the Terminal
Yard. The back walls of the abutments were not built until the steel had
been put in place.

No attempt was made to water-proof these abutments, but, in the rear of the
wall, open spaces were left, about 6 ft. from center to center, which were
connected with drain pipes at the base of and extending through the wall,
for the purpose of carrying off any water that might develop in the rock.
These drains were formed by building wooden boxes with the side toward the
rock open and the joints in the boxes and against the rock plastered with
mortar in advance of the wall. A hose was used to run water through these
drains during the placing of the concrete, for the purpose of washing out
any grout which might run into them. Each box was washed out at frequent