published for the information and immediate action of the commanding officers of the various regiments and detachments:

The Third Pennsylvania Cavalry, Colonel Averell; First New York Cavalry, Colonel McReynolds; Fourth Pennsylvania Cavalry, Colonel Childs, are assigned to the First Brigade, Colonel William W. Averell commanding.

The Eighth Illinois Cavalry, Lieutenant-Colonel Gamble; the Eighth Pennsylvania Cavalry, Colonel Gregg, and the Sixth New York (two squadrons), Lieutenant-Colonel McVicar, to the Second Brigade, Colonel D. McM. Gregg commanding.

Barker's squadron is assigned to the First [Second] Corps a' Armee, General Sumner.

De Laney's [?] squadron, Fifth Pennsylvania Cavalry, to the Second [Third] Corps, General Heintzelman.

One squadron of the Eighth Illinois to the Third [Fourth] Corps, General Keyes.

One squadron of the First New York to the Fourth [Fifth] Corps, General Porter.

One squadron of the First New York to the Fifth [Sixth] Corps, General Franklin.

2. The brigade commanders will make the details specified in the foregoing paragraphs at once.

3. Colonel Averell, commanding First Brigade, will keep the country in front of the right wing of the army and on its right thoroughly scouted over and patrolled by strong parties, and will make a daily report to these headquarters of the results of the operations of his brigade for the information of the general commanding the Army of the Potomac.

4. Colonel Gregg, commanding Second Brigade, will do the same in regard to the left wing of the army, making the same reports daily as called for from Colonel Averell.

5. Colonel Rush will see that his regiment both officers and men, become thoroughly acquainted with all the country in the vicinity of this army, and detail an officer and 20 men to report daily at the headquarters of each army corps, to act as guides in that corps.

6. Each company will be allowed but one wagon, and in addition one wagon will be allowed to the officers of a squadron and one for the field and staff. All transportation over this in the regiment will be turned over to the quartermaster-in-chief of this army.

7. Brigade commanders will see that the regiments in this brigade are so located that they can have open country to form in, and, if possible, on main avenues of communication.

8. The whole regular cavalry will be consolidated into as many complete squadrons as the numbers present will allow, and the officers will be assigned to each as the interests of the service may demand.

By order of Brigadier-General Stoneman, commanding division:

A. J. ALEXANDER.

First Lieutenant, Fifth Cavalry, Acting Assistant Adjutant-General.

HEADQUARTERS ARMY OF THE POTOMAC.

July 9, 1862-3 p.m. (Received 10.45 p.m.)

Honorable E. M. STANTON, Secretary of War;

General Davidson found enemy's rear guard 4 miles off on Long Bridge road this morning. Several prisoners confirm previous state-