=Strutting.=--When the rock was seamy and full of fissures, running in every direction, it was necessary to support the roof of the excavation. This was done in the following manner: After part 4 was removed the timbers supporting the roof of the excavation were set up. In this case, the polygonal strutting was used. This consisted of heavy timber frames placed transversely to the axis of the tunnel and supporting the planks or poling-boards which ran longitudinally against the roof of the excavation. The seven-segment arch frame was used in the Murray Hill tunnel. At the bottom of part 4 were placed longitudinally 12 × 16 in. beams and upon them rested the inclined segments which, with a horizontal one, formed the arch frame as shown in Fig. 60. When the pressures were too heavy the crown segment was reinforced by a 6 × 12 in. beam, kept in place by two 12 × 12 in. inclined props which rested on the templates. As the tunnel was lined with concrete, the timbering was left in place and it was built outside the line of the extrados of the concrete lining. Timbering was only used for a short distance but it necessitated a larger amount of rock excavation when it was required. [Illustration: FIG. 60.--Timbering Used in the Murray Hill Tunnel.] =Hauling.=--Great efficiency was shown in the method of hauling away the excavated materials. Three narrow-gauge parallel tracks were laid on the floor of the tunnel and extended to the faces of the advance drifts. Small flat cars were run on these tracks. They carried steel boxes, 5 ft. square and 15 ins. deep, fitted with three lifting rings and chains. When filled, the cars were run to the bottom of the shaft, the boxes were hoisted by a stiff-legged derrick placed at the shaft head, and the débris was dumped into storage bins of 300 cu. yds. capacity. These bins were elevated 8 ft. above the street so that the wagons could be driven under it to take loads of spoil by means of chutes. The broken rock was loaded into the boxes by hand. =Concrete Lining.=--The tunnel was lined with concrete which was manufactured by a quite elaborate plant. A stone crushing plant, consisting of bins for raw and crushed stone, was erected at the shaft head and a mixing plant was suspended from the shaft. On the platform of the shaft head were two bins side by side, one for crushed stone, the other for sand; both of which communicated, by means of trap doors, with a hopper chute. The materials from the hopper were delivered into a measuring box where cement was laid on top of the other ingredients by hand. They were then conveyed through a canvas chute into a cubical mixer operated by an engine. The mixer discharged its contents into skips set on cars at the bottom of the shaft and the concrete was hauled inside the tunnel ready for use.