MANASSAS, August 20, 1863.

General KING:

Information has been received here that a force of cavalry crossed United States Ford this a. m., between 10 and 11 a. m. Heavy musketry firing was heard in the direction of Elkton. General Slocum has sent this word to headquarters. Cavalry can approach us both by way of Dumfries either to Bristoe, here, or Union Mills, Fairfax, or toward Alexandria. I think they would go pretty low down. No cavalry here.

ALFRED GIBBS,

Colonel.

MORRISVILLE, August 20, 1863.

Major-General HUMPHREYS:

A report from Elk run confirms the statement of heavy skirmishing, with no artillery, about 10 a. m. for about one hour, about 5 miles east of Elk Run. General Kilpatrick's communication has no hour mentioned to show when it was written. I do not see how an enemy could have passed between him and me, but the skirmish firing is unexplained. It would be well to warn the guards between you and Alexandria.

G. K. WARREN,

Major-General.

AUGUST 20, 1863-6 p. m.

Brigadier General RUFUS KING,

Commanding Division, Centreville:

I am instructed by the major-general commanding to inform you that recent information derived from scouts and spies indicate the probability of a strong raid,or some similar movement, on the part of the enemy from the vicinity of the United States Ford.

Very respectfully, your obedient servant,

A. A. HUMPHREYS,

Major-General, and Chief of Staff.

HEADQUARTERS TWELFTH ARMY CORPS, August 20, 1863.

Major-General HUMPHREYS:

It is reported by Lieutenant-Colonel Johnstone, Fifth New York Cavalry, said to be at Ballard's Dam, that a large body of the enemy's cavalry crossed below him and passed northward. This reaches me through General Greene, who is at Elli's Ford.

H. W. SLOCUM,
Major-General.

HEADQUARTERS ARMY OF THE POTOMAC, August 20, 1863.

Major-General SCHURZ, Commanding Eleventh Corps:

General Kilpatrick telegraphs that Lieutenant-Colonel Johnstone denies the report that any cavalry has crossed the river; that the