The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

Canvas pontoon boats.

When dismantled, the canvas pontoon boats occupied a surprisingly small space. Thus the capacity of a train for bridge material of this kind was very much greater than for that of the wooden pontoons. The latter, however, gave better and more lasting service. The canvas became water-tight if well soaked. These pontoon boats were “knocked down” to be transported; the canvas was folded into a compact bundle and stowed in one of the wagons of the train. The parts of each boat were always kept together, so that they could be assembled at any time. The canvas, all in one piece, was laid out smooth on the ground, the bottom pieces of the frame put in place, the tenons of the uprights and the braces inserted in their corresponding mortises, the gunwales together with the end-pieces placed on the top, and the canvas then brought up over the sides and lashed tightly over the gunwales, by ropes eye-spliced into the eyes of the sides. The inside end-pieces were then carried around the bow and stern and lashed, and the outer pieces brought up over the ends and lashed in the same manner as the sides. The boat was then allowed to soak in the water for a time. Each boat was twenty-one feet long, five feet wide, and two and a half feet deep.

A canvas pontoon boat assembled ready for business--March, 1864	Canvas pontoon bridge, North Anna river
The Bridge from upstream, Jericho mills