Lee thus obtained exact and detailed information of the position of McClellan's army, and he laid out his campaign accordingly. Meanwhile his own forces in and about Richmond were steadily increasing. He was planning for an army of nearly one hundred thousand and he now demonstrated his ability as a strategist. Word had been despatched to Jackson in the Shenandoah to bring his troops to fall upon the right wing of McClellan's army. At the same time Lee sent General Whiting north to make a feint of joining Jackson and moving upon Washington. The ruse proved eminently successful. The authorities at Washington were frightened, and McClellan received no more reënforcements. Jackson now began a hide-and-seek game among the mountains, and managed to have rumors spread of his army being in several places at the same time, while skilfully veiling his actual movements. It was not until the 25th of June that McClellan had definite knowledge of Jackson's whereabouts. He was then located at Ashland, north of the Chickahominy, within striking distance of the Army of the Potomac. McClellan was surprised but he was not unprepared. Seven days before he had arranged for a new base of supplies on the James, which would now prove useful if he were driven south of the Chickahominy. On the very day he heard of Jackson's arrival at Ashland, McClellan was pushing his men forward to begin his siege of Richmond--that variety of warfare which his engineering soul loved so well. His advance guard was within four miles of the Confederate capital. His strong fortifications were bristling upon every vantage point, and his fond hope was that within a few days, at most, his efficient artillery, for which the Army of the Potomac was famous, would be belching forth its sheets of fire and lead into the beleagured city. In front of the Union encampment, near Fair Oaks, was a thick entanglement of scrubby pines, vines, and ragged bushes, full of ponds and marshes. This strip of woodland was less than five hundred yards wide. Beyond it was an open field half a mile in width. The Union soldiers pressed through the thicket to see what was on the other side and met the Confederate pickets among the trees. The advancing column drove them back. Upon emerging into the open, the Federal troops found it filled with rifle-pits, earthworks, and redoubts. At once they were met with a steady and incessant fire, which continued from eight in the morning until five in the afternoon. At times the contest almost reached the magnitude of a battle, and in the end the Union forces occupied the former position of their antagonists. This passage of arms, sometimes called the affair of Oak Grove or the Second Battle of Fair Oaks, was the prelude to the Seven Days' Battles.