diagonal braces. To each pair of soldiers a floor template, _T_, was
then nailed. The form for the center drain was then suspended as shown
in Fig. 1, Plate LXXIV. Three pieces of shuttering, _FFF_, 20 ft. long,
were then nailed to the bottom of the soldiers. One is all that would
have been needed for the first concrete placed, but it was easier to
place them at this stage than later, when there was less room. Three
rough shutters were also nailed to the curved portion for the floor
template. Opposite each biat, a bracket, _bb_, was then nailed, which
carries a set of rough boards which formed the risers for the duct
steps. Everything was then ready for concreting except that, where
refuge niches occurred, a form for the portion of the niche below the
seat was nailed to the shuttering. This form is shown at _R_ in Fig. 1,
Plate LXXIV.

[Illustration: PLATE LXXIV]

The concrete was dumped down on each side from side-dump cars standing
on the track, and, falling between the risers for the duct steps, ran or
was shoveled under the forms and down into the bottom. The horizontal
surface on each side the center drain was smoothed off with a shovel.
The workmen became very skillful at this, and got a fairly smooth
surface. This concrete was usually placed in lengths of 45 or 60 ft.
After setting for about 24 hours, the brackets, _bb_, were removed,
together with the shuttering on the steps. The triangular pieces, _t_ in
Fig. 1, Plate LXXIV, were not removed until later. Instead, a board was
laid upon this lower step on which the duct layers could work. This and
the triangular piece were not removed until just before the bench
concrete was placed. This was important, as otherwise the bond between
the old and new concrete would be much impaired by dirt ground into the
surface of the old concrete. The ducts were then laid, as shown in Fig.