Meanwhile the Federals were covertly engaged in an undertaking which was fated to result in conspicuous failure. Some skilled miners from the upper Schuylkill coal regions in the Forty-eighth Pennsylvania attached to the Ninth Corps were boring a tunnel from the rear of the Union works underneath the Confederate fortifications. Eight thousand pounds of gunpowder were placed in lateral galleries at the end of the tunnel. At twenty minutes to five on the morning of July 30th, the mine was exploded. A solid mass of earth and all manner of material shot two hundred feet into the air. Three hundred human beings were buried in the débris as it fell back into the gaping crater. The smoke had barely cleared away when General Ledlie led his waiting troops into the vast opening. The horror of the sight sickened the assailants, and in crowding into the pit they became completely demoralized. In the confusion officers lost power to reorganize, much less to control, their troops. The stunned and paralyzed Confederates were not long in recovering their wits. Batteries opened upon the approach to the crater, and presently a stream of fire was poured into the pit itself. General Mahone hastened up with his Georgia and Virginia troops, and there were several desperate charges before the Federals withdrew at Burnside's order. Grant had had great expectations that the mine would result in his capturing Petersburg and he was much disappointed. In order to get a part of Lee's army away from the scene of what he hoped would be the final struggle, Hancock's troops and a large force of cavalry had been sent north of the James, as if a move on Richmond had been planned. In the mine fiasco on that fatal July 30th, thirty-nine hundred men (nearly all from Burnside's corps) were lost to the Union side. The Confederate loss was about one thousand. In the torrid days of mid-August Grant renewed his attacks upon the Weldon Railroad, and General Warren was sent to capture it. He reached Globe Tavern, about four miles from Petersburg, when he encountered General Heth, who drove him back. Warren did not return to the Federal lines but entrenched along the iron way. The next day he was fiercely attacked by the Confederate force now strongly reënforced by Mahone. The assault was most sudden. Mahone forced his way through the skirmish line and then turned and fought his opponents from their rear. Another of his divisions struck the Union right wing. In this extremity two thousand of Warren's troops were captured and all would have been lost but for the timely arrival of Burnside's men.