[226] during this period no military movement occurred, with the exception of a raid into Pennsylvania by Stuart. About the middle of October, that enterprising officer, with twelve or fifteen hundred troopers, crossed the Potomac above Williamsport, passed through Maryland, penetrated Pennsylvania, occupied Chambersburg, where he burnt considerable government stores, and after making the entire circuit of the Union army, recrossed the Potomac below the mouth of the Monocacy. He was all the way closely pursued by Pleasonton with eight hundred cavalry, but though that officer marched seventy-eight miles in twenty-four hours, he was unable to intercept or overtake his fast-riding rival.
On the recrossing of the Potomac by Lee after Antietam, McClellan hastened to seize the debouche of the Shenandoah Valley, by the possession of Harper's Ferry. Two corps were posted in its vicinity, and the Potomac and Shenandoah spanned by ponton-bridges. At first McClellan contemplated pushing his advance against Lee directly down the Shenandoah Valley, as he found that, by the adoption of the line east of the Blue Ridge, his antagonist, finding the door open, would again cross to Maryland. But this danger being removed by the oncoming of the season of high-water in the Potomac, McClellan determined to operate by the east side of the Blue Ridge, and on the 26th his advance crossed the Potomac by a ponton-bridge at Berlin, five miles below Harper's Ferry. By the 2d November the entire army had crossed at that point. Advancing due southward towards Warrenton, he masked the movement by guarding the passes of the Blue Ridge, and by threatening to issue through these, he compelled Lee to retain Jackson in the Valley. With such success was this movement managed, that on reaching Warrenton on the 9th, while Lee had sent half of his army forward to Culpepper to oppose McClellan's advance in that direction, the other half was still west of the Blue Ridge, scattered up and down the Valley, and separated from the other moiety by at least two days march. McClellan's next projected move was to strike across obliquely westward and
