500 yards long, similar to the model bridge at the Volunteer Engineer camp at Hilton Head.
4. This bridge is represented in Plate I. Fig. 1 is a general elevation; Fig. 2, plan; Fig 3, a cross-section; Fig. 4, the method of securing the floor beams to the uprights; Fig. 5, an enlarged figure, showing the method of holding the floor boards a in place; b is a strip, 1 1/2 inches by 5 inches, which is lashed over the floor planks; Fig. 6 presents the shoe used at the bottom of the trestle, to prevent it sinking too deep into a muddy bottom; c is the know used in the lashing.
5. July 2.-Got ready the suspension bridge, leaving this matter particularly in charge of Lieutenant Hiram Farrand, Volunteer Engineers. The span of the bridge is 200 feet. New towers of timber work have to be made, which were planned, and instructions left with Major Butt to have Lieutenant Farrand make them as soon as possible, and ship the bridge with the trestle bridge and engineer tools.
6. July 3.-Continued building the trestle bridge day and night, with a detail of 75 engineers and 150 infantry. Major Butt in charge.
7. Had a large party of engineers repairing the pontoon train Numbers 7.
8. July 4.-Getting the bridges and pontoons ready, and repairing all the boats and scows that can be found.
9. July 5.-Same work as yesterday. Some delay for want of lumber.
10. July 6.-Fourteenth hundred feet of the trestle bridge nearly ready to ship. Suspension bridge and boats progressing.
11. July 7.-Began to shop the bridges on the steamer General Meigs. Some deadly for want of timber. At work until midnight getting tools and materials shipped; then left with the commanding general, on board the Mary Benton, for Folly Island, taking the saws for cutting piles under water, on this steamer, having given Major Butt, Volunteer Engineers, instructions to ship the remainder of the bridges and tolls.
12. July 8.-Arrived in Folly River at 10 a. m.
13. Orders were received to remove as many of the piles in the Folly River, at the point indicated on the general maps, as would admit the passage of the largest launches and the large scows.
14. This was done the same night, by sawing them off under water, at a depth of 8 feet below low tide. Plate II shows the machinery used.
15. Fig. 1 represents a front view of the saw, and Fig. 2 shows a side elevation; Fig. 3, the general disposition in plan.
16. The saw is worked by boring a hole in the pile to be sawed off, at the proper height above water, and in this hole an iron pin is inserted, upon which the saw-frame vibrates. Ropes from the rings at either end of the saw are taken to boats properly anchored, or held, as they were in this case, by sharp-pointed poles, b b, thrust into the sand at the bottom of the river. At a given signal, the ropes are pulled alternately, and the saw vibrated.
17. In this way, a pile 10 or 12 inches in diameter was cut off in an average length of time of from six to seven minutes; including the change from one pile to another, about ten minutes were occupied.
18. The piles were driven in two rows, alternating with one another, 4 feet apart in each row. The rows were 3 feet apart. Three piles had been taken out previously, or a space of about that extent