Headquarters Eleventh CORPS, Middletown, Md.,

June 28, 1863-11 a. m.

Major-General BUTTERFIELD,

Chief of Staff, Army of the Potomac:

GENERAL: A man of one of General Stahel's scouting parties has just returned from Hagerstown. He entered the town at 10 p. m. last night. A squad of Stuart's cavalry had passed through an hour before. The main body of General Stuart's cavalry was encamped last night between Williamsport and Hagerstown at the break of day. Citizens report that the rebels are driving cattle and horses toward Williamsport; he saw a drove of them. Inclosed find copy of report from outposts at Boonsborough Gap.

I am, general, respectfully, your obedient servant,

CHAS. W. ASMUSSEN,

Lieutenant Colonel, and Chief of Staff, Eleventh Corps.

[Inclosure.]

SIGNAL STATION, South Mountain,

June 27, 1863-2 p. m.

Brigadier General A. VON STEINWEHR,

Commanding Second Division, Eleventh Corps:

GENERAL: I have the honor to report that I can see no camps in or around Hagerstown or in any other direction. There is a dense smoke rising from a point above Williamsport, across the Potomac. I can see no infantry marching in any direction. Saw a body of cavalry, probably 25 in number, in a field beyond Sharpsburg, apparently reconnoitering; they are not now in sight. Also a body somewhat larger moving out of Hagerstown by a road leading northward. There is what appears to be a small picket of 25 or 30 men in a field this side of Hagerstown, along the road leading from that place to Boonsborough, but of this I am not positive-cannot make it out clearly. Can clearly distinguish the roads leading from Boonsborough to Hagerstown, Sharpsburg, and Shepherdstown, and can see no troops moving upon them, excepting the Union cavalry now at hand. The Union cavalry are on the road to Hagerstown. Boonsborough, Hagerstown, Sharpsburg, Shepherdstown, Keedysville, and Funkstown can plainly be seen from this place. There is smoke rising just now beyond Hagerstown, as of a house burning.

I have the honor to remain, your obedient servant,

L. M. BUCHWALTER,

Captain Seventy-third Ohio Volunteers.

Headquarters Army of the Potomac, June 28, 1863-11. 45 a. m.

Commanding Officer First Corps:

The commanding general directs that the three corps of your command march to the vicinity of Frederick to-day and encamp. Their arrival here will be reported by a staff officer.

Very respectfully, &c.,

S. WILLIAMS,

Assistant Adjutant-General.