rely filled with neat cement grout.

_Box Drains._--Various methods of forming the box drains were considered,
such as using half-tile drains, or a metal form, or a collapsible form
which could be withdrawn, but it was finally decided to build boxes in
which the side toward the rock was open and the joints in the boxes and
against the rock were plastered with cement mortar. These boxes were left
in place. Fig. 1, Plate LI, shows the tie-rods and box drains in place, and
holes being cut near the bottom of the drains for the pipes leading through
the wall.

_Forms._--Fig. 1, Plate LI, shows the form used on the south side of the
work. The materials were of good quality, and the form, which was about 50
ft. long, was used to build twelve sections, or about 600 ft. of wall. The
form was tied in at the top and bottom by cables attached to rods drilled
into the rock, and it was thought that, with the trusses to stiffen the
middle section of the form, it would not be necessary to use raker braces
against it. This would have been desirable, as the placing of the raker
braces took considerable time. It was found, however, that the form was not
sufficiently rigid, as it bulged at the middle section and could not be
held by the trusses. Two or three sets of raker braces, about 12 ft. apart,
were used, and in addition, rods with turnbuckles were placed through the
form and fastened to the tie-rods, and thus the form was held in place
successfully. On the forms built later, the trusses were omitted, and raker
braces, about every 6 ft., were used. The rods which screwed into the
turnbuckles were removed before the form was moved. The photograph, Fig. 4,
Plate LII, was taken inside the concrete form for the lower face wall on
the north side, and shows the drains leading through the wall, the
turnbuckles attached to the tie-rods, the cables attached to rods in the
rock, and the braces to keep the form from coming in; these braces, of
course, were removed as the concrete came up. The form was built low and
wedged up into position. After a section of concrete had set sufficiently,
the wedges were knocked out, the form was lowered and moved from the wall,
and was then moved along the lowest waling piece by block and tackle to its
new position.

Fig. 4, Plate L, shows the forms used on the north side of the work.

A section, 1 ft. square, at the top of the bridge seat of the lower face
wall, was left out, so that the bottom of the form f