The retreat of the enemy was conduced by several direct parallel roads, while our troops were compelled to march by difficult and circuitous routes. We were consequently unable to intercept him. General Hill arrived first at Bristoe, where his advance, consisting of two brigades, became engaged with a force largely superior in numbers posted behind the railroad embankment. The particulars of the action have not been officially reported, but the brigades were repulsed with some loss,and five pieces of artillery, with a number of prisoners, captured. Before the rest of the troops cold be brought up and the position of the enemy ascertained, he retreated across Broad Run. The next morning he was reported to be fortifying beyond Bull Run extending his line toward the Little River turnpike.

The vicinity of the intrenchments around Washington and Alexandria rendered it useless to turn his new position, as it was apparent that he could readily retire to them and would decline an engagement unless attacked in his fortifications. A farther advance was therefore deemed unnecessary, and after destroying the railroad from Cub Run southwardly to the Rappahannock the army returned on the 18th to the line of that river, leaving the cavalry in the enemy's front.

The cavalry of the latter advanced on the following day,and some skirmishing occurred at Buckland. General Stuart, with Hampton's division, retired slowly toward Warrenton, in order to draw the enemy in that direction, thus exposing his flank and rear to General Lee, who moved from Auburn and attacked him near Buckland. As soon as General Stuart heard the sound of Lee's gun he turned upon the enemy, who, after a stubborn resistance, broke and fled in confusion, pursued by General Stuart nearly to Hay Market, and by General Lee to Gainesville. Here the Federal infantry was encountered, and, after capturing a number of them during the night, the cavalry slowly retired before their advance of the following day.

When the movement of the army from the Rapidan commenced, General Imboden was instructed to advance upon the valley and guard the gaps of the mountains on our left. This duty was well performed by that officer,and on the 18th instant he marched upon Charlestown and succeeded, by a well-concerted plan, in surrounding the place and capturing nearly the whole stationed there, with all their stores and transportation. Only a few escaped to Harper's Ferry. The enemy advanced from that place in superior numbers to attack General Imboden, who retired, bringing off his prisoners and captured property, his command suffering very little loss and inflicting some damage upon the pursuing columns.

In the course of these operations, 2,436 prisoners were captured, including 41 commissioned officers. Of the above number, 434 were taken by General Imboden.

A more complete account, with a statement of our loss in killed, wounded, and prisoners, will be forwarded as soon as the necessary official reports shall have been received

Very respectfully, your obedient servant,

R. E. LEE,

General.

General S. COOPER,

Adjutant and Inspector General, Richmond, Va.