HEADQUARTERS THIRD DIVISION, CAVALRY CORPS, August 20, 1863.

Brigadier General G. A. CUSTER, Commanding Second Brigade:

GENERAL: You will send your entire train (every wagon) to Hartwood Church at once. You will hold your command in readiness to move at a moment's notice. Observe the greatest vigilance, leaving your picket line and reserves as they now are. Word has just come in from the right of our line confirming your report of this morning. I believe the rebel army is about to advance.

Very respectfully,
J. KILPATRICK,

Brigadier-General of Volunteers.

HEADQUARTERS CAVALRY CORPS, August 20, 1863.

Brigadier-General GREGG, Commanding Second Cavalry Division:

GENERAL: The major-general commanding directs me to inform you that there is a rumor that Stuart, with all his cavalry except Lee's brigade, is in the valley. The general desires that you will direct your cavalry to keep a close lookout in the direction of the gaps.

Very respectfully, your obedient servant,

C. ROSS SMITH,

Lieutenant-Colonel, Chief of Staff.

HEADQUARTERS THIRD DIVISION, CAVALRY CORPS, Hartwood Church, Va., August 20, 1863.

Captain A. J. COHEN,
Assistant Adjutant-General, Cavalry Corps:

CAPTAIN: I have the honor to report the following, received from my picket line up 2 p. m.:

Opposite Falmouth the enemy's picket line has been much weakened during the night, but few encampments can be seen in that vicinity, and everything indicates a movement of the enemy in some direction- I think to my right. General Custer reports a long column of dust, some 4 miles in length, moving in the rear of Fredericksburg, and a complete silence is kept by their men on picket. Near United States Ford the enemy have a few pieces of artillery in position, and a large body of cavalry were reported near this ford this morning. From the latest I can gather, this cavalry force is moving to my right. It is believed by the enemy that our army is retiring upon Centreville and Alexandria. All the fords along my river front are well guarded.

Very respectfully,

J. KILPATRICK.

[Indorsement.]

HEADQUARTERS CAVALRY CORPS, August 20, [1863] - 9 p. m.

Respectfully forwarded to Major-General Humphreys, chief of staff.

This report confirms those of this morning, that the rebel army is on the move. It looks toward Richmond.

A. PLEASOTON,
Major-General, Commanding.