HDQRS. CAVALRY BRIGADE, THIRD ARMY CORPS, Camp near Culpeper, Va., August 14, 1862.

SIR: I have the honor to make the following report of the operations of the cavalry brigade under my command on on the 8th and 9th of August, just passed:

On the 7th my line of pickets extended from a point 3 miles east of the railroad to beyond Barnett's Ford some 3 or 4 miles, and on that day I rode along the entire length of that picket line, examining the headquarters of the pickets and seeing that the vedettes in front were properly executing their duty.

About 12 o'clock that night Captain David Gardner, First Pennsylvania Cavalry, in charge of the line of pickets west of Robertson's River, reported that his vedettes and pickets had all been driven in; that the enemy had crossed the Rapidan in force, and that he (Captain Gardner) was filling back toward Robertson's River. I immediately dispatched Colonel Owen Jones with the remainder of his regiment to re-enforce the pickets, and he shortly reported that he had advanced again to within a couple of miles of the river.

Before the breach of day Lieutenant-Colonel Karge, with 160 of the men of his Jersey regiment, started, in order to turn the enemy's left, by the madison road, leading into the Barnett's Ford road, while I, with the remainder of the regiment, under Major Beaumont, advanced to re-enforce Colonel Jones and attack the enemy in front.

I advanced all the way to the Rapidan, and Major Beaumont's vedettes here came in sight of a large train of the enemy's and their camp, with a heavy force of cavalry in front. Just at this moment a contraband come in, and reported that the whole of Ewell's division had crossed the Rapidan, and were advancing. I ordered Major Beanmont to fall back slowly when pressed by the enemy and sent word to Colonel Karge to return at once, as the enemy were in too great force to be attacked by our light force.

The Jersey battalion fell back slowly and in good order, and about 3 miles from the ford I relieved it by bringing up the Pennsylvania regiment into action. I fell back to the road on which Colonel Karge was obliged to return, halted my command, and held that position until Colonel Karge returned with his force and 20 rebel prisoners, captured by Captain Janeway, Company L, New Jersey cavalry. During that time we had to stand a heavy fire from the enemy's cavalry, in which we lost two corporals of the Pennsylvania regiment, severely wounded.

As soon as Colonel Karge came in I continued my retreat. The enemy now opened upon us with their artillery, and we crossed Robertson's River under heavy fire of both artillery and musketry.

Colonel Owen Jones, First Pennsylvania Cavalry, here by my order destroyed the bridge, which for a long time prevented the crossing of the river by the enemy's artillery.

As soon as I had discovered the enemy's force I had sent to camp and had everything started for Culpeper.

Owing to the neglect of duty of Quartermaster Hazen the New Jersey trains left their portable forge and a great deal of baggage.

I continued the retreat to Cedar Run, where I posted the Pennsylvania cavalry on picket, and fell back a mile farther with the Jersey regiment. I had sent word to the pickets on the cast side of Robertson's River to fall back, but the order reaching them so late it was impossible to do so. They remained in the woods till the next day, when they succeeded in getting back to Culpeper.

Captain Boyd, the