Numbers 14. CENTREVILLE, September 1, 1862-12 m.

Major-General McDOWELL:

You will march rapidly back to Fairfax Court-House with your whole division, assume command of the two brigades now there, and immediately occupy Germantown with your whole force, so as to cover the turnpike from this place to Alexandria. Jackson is reported advancing on Fairfax with 20,000 men. Move rapidly.

JNO. POPE,

Major-General, Commanding.

Numbers 28. Report of Brigadier General John P. Hatch, U. S. Army, commanding First Division, of the battles of Groveton and Bull Run.

CAMP NEAR FREDERICK, MD., September 13, 1862.

CAPTAIN: I have the honor to submit the following report of the movements of the First Division, Third Corps, temporarily under my command during parts of the 29th and 30th days of August:

Late on the afternoon of the 29th ultimo I was ordered by General McDowell in person (who was at the time stationed near the stone house, on the turnpike from Gainesville to Centreville) to move the division on the Gainesville road in pursuit of the enemy, who, he informed me, were retreating. Gibbon's brigade had been detached to support some batteries. With the three other brigades of the division and Gerrish's battery of howitzers I proceeded with all the speed possible, hoping by harassing the enemy's rear to turn their retreat into a rout.

After marching about three-quarters of a mile the Second Regiment of U. S. Sharpshooters was deployed to the front as skirmishers, the column continuing up the road in support. The advance almost immediately became warmly engaged on the left of the road. Two howitzers were then placed in position, one on each side of the road, and Doubleday's brigade was deployed to the front, on the left of the road, and moved up to the support of the skirmishers. We were met by a force consisting of three brigades of infantry, one of which was posted in the woods on the left, parallel to and about an eighth of a mile from the road. The two other brigades were drawn up in line of battle, one on each side of the road. These were in turn supported by a large portion of the rebel forces, estimated by a prisoner, who was taken to their rear, at about 30,000 men drawn up in successive lines, extending 1 1/2 miles to the rear. Doubleday's brigade moved to the front under a very heavy fire, which they gallantly sustained; but the firing continuing very heavy, Hatch's brigade, commanded by Colonel Sullivan, was also deployed and moved to the support of General Doubleday. Patrick's brigade, which has been held in reserve, took up a position on the opposite side of the road, completely commanding it. The struggle, lasting some three-quarters of an hour, was a desperate one, being in many instances a hand-to-hand conflict.

Night had now come on, our loss had been severe, and the enemy occupying a position in the woods on our left which gave them a flank fire upon us, I was forced to give the order for a retreat. The retreat was executed in good order, the attempt of the enemy to follow being defeated by a few well-directed volleys from Patrick's brigade.