Through July one of Burnside's regiments, composed of Pennsylvanians used to such business, had been working at a mine under one of the main redoubts in front of Petersburg. A shaft 500 feet long was dug, with a cross gallery 80 feet in length at the end square under the redoubt. This chamber was charged with 8,000 pounds of powder, which was fired July 30th. The battery and brigade immediately overhead were blown into the air, and the Confederate soldiers far to left and right stunned and stupefied with terror. For half an hour the way in to Petersburg was open. Why did none enter? The answer is sad. Grant had splendidly fulfilled his part by a feint to Deep Bottom across the James, which had drawn thither all but about one division of Lee's Petersburg force. But Meade, at a late hour on the 29th, changed the entire plan of assault, which Burnside had carefully arranged, and to lead which a fresh division had been specially drilled. Then there was lamentable inefficiency or cowardice on the part of several subordinate officers. The troops charged into the great, cellar-like crater, twenty-five feet deep, where, for lack of orders, they remained huddled together instead of pushing on. The Confederates rallied, and after shelling the crater till more of its occupants were dead than alive, charged and either routed the living or took them prisoners. [Illustration: Map.] The Shenandoah Valley. During the summer and fall of 1864 the scene of active operations was shifted to the Shenandoah Valley. The latter part of June Lee sent Early, 20,000 strong, to make a demonstration against Washington, hoping to scare Grant away from Petersburg. Early moved rapidly down the valley, hustling Hunter before him, who escaped only by making a detour to the west, thus leaving Washington open. Thither Early pushed with all speed. General Lew Wallace hastily gathered up the few troops at his disposal and hurried out from Baltimore to meet him. Wallace was defeated at the Monocacy River July 9th, but precious time was gained for the strengthening of Washington. When Early arrived before the city on the 11th, Grant's re-enforcements had not yet come, and the fate of the capital trembled in the balance. Early happily delayed his attack till the morrow, and that night two of Grant's veteran corps landed in Washington, President Lincoln, in his anxiety, being on the wharf to meet them. Once more Washington was safe, and Early fell back, pressed by the newcomers. [Illustration: Map.] General Early's Maryland Campaign.