In the method used, in the center of each charge was placed the end of a length of Gomez fuse, cut at different points to allow the flame to ignite the powder in several places. This fuse was then grafted to an equal length in the same level running to the other mine. The three mines in the upper level were joined in the same way and, finally, the two lines were grafted together and joined to the end of a piece of slow-match cut to burn twenty minutes. The grafts had been tried repeatedly before being finally determined on, and had always been successful.
On exploding the mine the embankment was thrown down and a current commenced running through the canal. Excavation by means of discharging cans of powder under water deepened and widened the channel, aided by strong freshest, so that at high water six and a half feet of water is on the embankment. General Butler having been relieved from the department about this time, work was discontinued by order.
The canal at present is used by the steamer O. S. Pierce and others of that class, which save by this way about five miles and a half of travel. A few days" work to clear up the disturbed mass and to widen and deepen the north mouth would make this the usual traveled route by all vessels navigating the river. The current and tide partly flow through this way, but their action is unimportant in clearing it out, because the debris consists of large lumps of cemented gravel and hard blue clay. The above embraces all the data of interest in this much-talked-of project, and is given complete to avoid referring to it in the account of each month's labor.
September.-During the month a line of works was built and a post established at Harrison's Landing. The defensive works consisted of a redoubt of four embrasures, with a stockaded gorge commanded by the gun-boats in the river, and infantry breast-works running from the flanks to the river. The length of the whole line is 1,412 yards. A canvas pontoon bridge of twenty-three boats was built on the Appomattox River September 19. The pensioners who built it, having no experience with these boats, were twelve minutes in building the first and three minutes in building the last, the average time being seven minutes and a half for each boat. Owing to the river being affected by the tide, the claw balks had to be lashed to the saddle piece, or they would slip up or down, according as the tide was ebb or flow. Often this bridge had to be covered with manure to deaden the sound of travel when troops crossed. In these cases the dust of the manure falling into the canvas boats would rot the threads of the canvas and cause more or less leakage. It was noticed that some of the canvas coverings would leak as much as six inches of water at night and none the following day. Teams heavily loaded would often sink these boats to within four inches of the gunwale. These were among the most prominent things noticed in the use of these boats in a permanent bridge, a use, however, for which they were never intended.
During the night of September 28 a pontoon bridge 1,320 feet long was built on the James River at Aiken's Landing. With 100 pensioners the bridge was finished in six and a half hours, so quietly as not to disturb the enemy's pickets on the opposite side of the river.
The army began to cross at 3 a. m. September 29 in two columns, one on the bridge above spoken of and the other on the bridge at Deep Bottom. A successful advance was made; Fort Harrison, the key point of the outer line of Richmond defense, carried by assault, and the line of works extending to the Darbytown road occupied by