Before Petersburg.on July 30, 1864, at the exploding of the hidden mine under Elliott's salient, the strong Confederate fortification opposite. The plan of the mine was conceived by Colonel Henry Pleasants and approved by Burnside, whose Ninth Corps, in the assaults of June 17th and 18th, had pushed their advance position to within 130 yards of the Confederate works. Pleasants had been a mining engineer and his regiment, the forty-eighth Pennsylvania, was composed mainly of miners from the coal regions. The work was begun on June 25th and prosecuted under the greatest difficulties. In less than a month Pleasants had the main gallery, 510.8 feet long, the left lateral gallery, 37 feet long, and the right lateral gallery; 38 feet long, all completed. While finishing the last gallery, the right one, the men could hear the Confederates working in the fortification above them, trying to locate the mine, of which they had got wind. It was General Burnside's plan that General Edward Ferrero's division of colored troops should head the charge when the mine should be sprung. The black men were kept constantly on drill and it was thought, as they had not seen any very active service, that they were in better condition to lead the attack than any of the white troops. In the upper picture are some of the colored troops drilling and idling in Camp after the battle of the Crater, in which about three hundred of their comrades were lost. The lower picture shows the entrenchments at Fort Morton, whence they sallied forth.