Meanwhile, Jackson's operations in the Shenandoah Valley had so startled and astounded the Federals that he was able to march, June 20-25, unobserved, over the passes of the Blue Ridge Mountains to Lee's assistance. A series of battles began June 26 at Mechanicsville on McClellan's right, near where Johnston had fought. But the failure of Jackson to arrive and begin the attack, according to agreement, caused the first Confederate onset to fail, with heavy losses to the South. The next day, however, the tide turned the other way and Lee routed McClellan at Gaines' Mill. McClellan now retreated across White Oak Swamp towards Harrison's Landing on the James. The weather was hot, the ground soft from rains, and the underbrush so thick and tangled that men could not see each other at a distance of ten paces, save in the narrow roads or small clearings. Realizing the difficulties under which his opponent labored, Lee ordered hasty pursuit, and ineffective blows were struck at Savage's Station and in White Oak Swamp. Jackson again failed to maintain the great reputation he had won in the Valley, and Magruder, Holmes, and Huger, other lieutenants of Lee, not knowing their own country as well as did the Federals, suffered their commands to be lost in the wilderness and thus aided McClellan in his escape from a dangerous situation. On July 1 the retreating Union army gathered, still devoted to its commander, on Malvern Hill, within support of the Federal gunboats in the James River below. The Confederates, confident and expectant, poured out of the woods from every direction, formed in battle array, and charged over open fields and rising ground toward the two hundred and fifty great guns which had been dragged for weeks through the swamps in the hope of just such an opportunity. The attempt of Lee to carry this impregnable position lost the Confederates as many brave men as all the other six days of unremitting warfare. McClellan held his own till night; Lee withdrew to the neighboring thickets, surprised at the resolute strength of an opponent who had avoided battle at every turn since June 26.