[Indorsement.]

HDQRS. FIRST CAV. BRIGADE, July 11, 1862.

Two squadrons Third Pennsylvania Cavalry went to within 3 miles of Long Bridge last night; encountered a light cavalry picket of the enemy; killed 1, dismounted 2, and captured 2 horses, 3 men, and went to within 6 miles of White Oak Swamp, without further signs of the enemy. After dark the vedettes fired upon some mounted people and fire was returned. The Lower Chickahominy has been thoroughly reconnoitered, without finding an enemy. The roads in that direction are generally laid down correctly on the maps. Captain McArthur, with a squadron of the Fifth United States, remained out on the Ninemile road last night and was re-enforced with a squadron of the First New York this morning, with instructions to move to on.

Respectfully,
WM. W. AVERELL,

Colonel, Commanding.

JULY 16, 1862. - Reconnaissance from Westover, on the Richmond Road.

Report of Colonel William W. Averell, Third Pennsylvania Cavalry, commanding First Cavalry Brigade.

HEADQUARTERS FIRST CAVALRY BRIGADE,
Westover, Va., July 17, 1862.

SIR: I have the honor to report that yesterday Captain Harrison, Fifth U. S. Cavalry, with two squadrons of his regiment, reconnoitered the Richmond road, which leaves the first Long Bridge road about 3 miles beyond its junction with the Charles City road. Upon the Richmond road he went about 4 miles, finding a picket of 25 cavalry and about two companies of infantry. From their maneuvers he was led to believe that they had artillery also. This impression was strengthened by the statement of a contraband, who informed him that they had cannon not far off. After a slight carbine skirmish, which resulted in the falling back of the rebel cavalry and in a display of the above-mentioned infantry force, he retired from that road, and proceeded to Saint Mary's Church, on the Long Bridge road. At that point he found a squadron of the Fourth Pennsylvania engaging in a desultory combat with about 100 rebel cavalry strongly positioned at a barn. Disposing a platoon under Lieutenant Byrnes to engage them at short range with a brisk fire, he proceeded to cut off the rebels by getting in their rear. Unfortunately he was discovered by them before he could reach the desired point, upon which they hastily mounted and commenced a disorderly retreat, which terminated in what is known as a skedaddle. He made a vigorous pursuit for some 3 or 4 miles to within a quarter of a mile of Long Bridge. Although three saddles of the enemy were emptied, Captain Harrison would not waste time in ascertaining if the riders were killed.

The duty of yesterday was very satisfactorily performed by Captain Harrison.

Last night 10 men were stationed with the infantry pickets on the first Long Bridge road, and 10 at Clarke's house, on the second road.

I am, respectfully, your obedient servant,

WM. W. AVERELL,

Colonel, Commanding.

Captain A. J. ALEXANDER, A. A. A. G.