Officers and non-commissioned officers to instruct the garrison you found under General Van Alen in the use of heavy guns, and have them prepare tables of ranges, &c., for them. I trust to your zeal and activity in this very trying moment.

They are fighting now on the Rappahannock. A general engagement is probably going on now.

GEO. B. McCLELLAN,

Major-General.

HEADQUARTERS ARMY OF THE POTOMAC, August 22, 1862.

Major General E. D. KEYES,
Commanding Fourth Army Corps:

The duty intrusted to your corps, while it is no doubt disagreeable, is of the utmost importance.

I fully realize how severe a tax it is upon men who have fought so gallantly and worked so hard as your corps to require them now to go upon fatigue duty. I feel sure, however, that if they knew that the work I now call upon them to perform is necessary they will perform it cheerfully. You will please detail as large working parties as the tools available will permit to perform the work laid out by the engineer officers.

It is a matter of vital importance that the details should be furnished and the work done in the shortest possible time.

I have taken all the necessary steps to have your command relieved by new troops at the earliest practicable moment.

It is imperatively necessary that the work required should be pushed with all the rapidity possible with the means at your command, and hold your command in readiness to move at the shortest notice.

If you judge it necessary, send two regiments or an entire brigade of infantry to Williamsburg to cover your operations.

Please push as far as possible the instruction of the old garrison in heavy artillery practice, and give me in full your views as to the best method of holding Williamsburg and the force necessary for that purpose.

Send a couple of squadrons of cavalry to Gloucester to patrol and examine the country on the left bank of the York.

If you think it advisable, send a much larger force of cavalry there for temporary duty. While we have a large cavalry force comparatively idle, it may be well to occupy a large portion of it in clearing out the country on that side of the York River.

If you think it best to occupy a point near Williamsburg by infantry, hold Fort Magruder and destroy the adjacent works.

Very respectfully, your obedient servant,

GEO. B. McCLELLAN,

Major-General, Commanding.

HEADQUARTERS ARMY OF THE POTOMAC, Steamer City of Hudson, off Fort Monroe, August 23, 1862.

Major General JOHN A. DIX,

Commanding Seventh Corps, Fort Monroe:

GENERAL: The general commanding directs me to inform you that the following movements have been ordered to take place immediately: