The concrete for the arches and bench-walls was loaded at the mixers into 1-yd., Stuebner, bottom-dumping buckets which just held a 4-bag batch. These buckets were placed on small flat cars, hauled into the tunnel, placed beneath the traveling gantry, as shown by Fig. 1, Plate XXIV, and hoisted to the platform above. These traveling gantries, the details of which are shown by Fig. 12, consisted essentially of platforms at each end of which an =A=-frame was erected; the latter supported at their apexes two =I=-beams, from the lower flanges of which was suspended a traveling block, shown at _A_, Fig. 12, and through which the hoisting rope was rigged. The buckets were hoisted through an opening in the platform and then moved along to where they could be dumped. The platforms were supported on wheels traveling on rails laid on the concrete of the foundation (for the bench-wall gantries) or on top of the bench-wall (for the arch gantries). Each of the first two of these traveling gantries used was equipped with a belt conveyor working on a cantilever arm, as shown by Figs. 3 and 4, Plate XXI, and Figs. 1 and 2, Plate XXIV. In using these belt conveyors, the concrete was dumped from the Stuebner bucket into a hopper, Fig. 1, Plate XXIV, with an adjustable slot in the bottom, under which the belt ran. [Illustration: Fig. 12. [Full Page] DETAILS OF TRAVELING GANTRY USED IN THE CONSTRUCTION OF THE TUNNEL LINING: SECTIONAL ELEVATION CROSS-SECTION A. DETAIL OF TRAVELING BLOCK B. DETAIL OF TOP SHEAVE C. DETAIL OF LOWER SHEAVE.] It was the original intention, in designing the conveyor, that the end of the cantilever arm should be swung from one side of the tunnel to the other, and that the traveler should be moved backward or forward, as might be required, and thus deliver the concrete from the end of the belt directly over the place in which it was to be deposited in the bench-walls. As a matter of fact, it was found impractical in operation to move the gantry readily, owing to its great weight, which was supported on only four ordinary car wheels and their bearings, and it was found more convenient to leave the arm in one position near the center, letting the concrete drop on the platform above the bench- or sand-wall forms, whence it could be shoveled into place, than to attempt to move it as had been intended. Both of these difficulties might possibly have been overcome by modifications in the design of the gantry and conveyor, had this method of handling the concrete seemed otherwise desirable.