No. 8. Report of Brigadier General Alfred Pleasonton, U. S. Army, commanding Cavalry Division, of operations September 4-17.

HEADQUARTERS CAVALRY DIVISION,
Camp near Sharpsburg, September 19, 1862.

GENERAL: I have the honor to submit the following report of service performed by this division in the late operations of the Army of the Potomac, comprehending the expulsion of the enemy from Maryland:

On the 4th instant the command moved from Falls Church, on the south side of the Potomac, passed over the Aqueduct Bridge to Tennallytown, and from thence proceeded to reconnoiter all the fords on the Potomac as far as Seneca Mills, finally assuming a position at Muddy Run. This occupied the 4th, 5th, and 6th instant.

On the 6th instant the First New York Cavalry moved to Middleburg, and sent four companies to occupy Clarksburg, at the same time scouting the country to Hyattstown. The First U. S. Cavalry proceeded to Brookville, to scout in the direction of the Baltimore and Ohio Railroad. The Eighth Illinois and Third Indiana Cavalry moved the same day in advance of Darnestown, picketing the roads in the direction of Poolesville and the fords on the Potomac.

On the 7th instant two squadrons of the Eighth Illinois and two of the Third Indiana, under Major Chapman, of the Third Indiana, made a dash on Poolesville and captured two cavalry vedettes, all of the enemy in the town at the time. The next day, the 8th instant, Colonel Farnsworth moved his command-the Eighth Illinois, Third Indiana, and a section of horse artillery of Company M, Second Artillery, under First Lieutenant Chapin-to occupy Poolesville and picket the roads to Donrad'd Ferry, Edwards Ferry, Barnesville, and the Monocacy. As this force neared Poolesville, the enemy's cavalry were observed retreating on the road leading to Barnesville, and some squadrons of the Third Indiana pushed after them. They had not proceeded far before the enemy opened a fire from some guns strongly posted on the right of the town. The section of artillery, under Lieutenant Chapin, soon silenced these guns, which made off in the direction of Barnesville. The squadrons of the Third Indiana, under Major Chapman, were now ordered to charge the battery, which was handsomely done, the enemy's cavalry and artillery being driven over 3 miles, when the Eighth Illinois coming up, under Major Medill, the chase was continued until after dark.

In this affair the Third Indiana lost 1 killed and 11 wounded; the Eighth Illinois 1 wounded. The rebel loss amounted to 8 killed, 16 wounded, and 6 prisoners-all cavalry.

On the 9th instant Farnsworth with his command proceeded toward Barnesville, and observing a squadron of the enemy's cavalry near Monacy Church, he directed Captain Farnsworth's squadron, of the Eighth Illinois, to gain their rear and cut them off. This movement succeeded dividing the enemy and in capturing their battle-flag (that of the Twelfth Virginia Cavalry, called the Ashby Cavalry), besides several prisoners. The march being continued toward Barnesville, Captain Kelley's squadron, Eighth Illinois, being in advance, encountered the enemy's vedettes on the edge of the village. A dash was made on them through the village and some 2 miles beyond, the troops being engaged twice in a hand-to-hand fight. The day's work resulted in killing 4 of