night. He wishes you to direct your cavalry to continue the pursuit vigorously, and to capture themif possible, and endeavor to keep between them and the Baltimore an Ohio Railroad. He wishes you to have your command ready at all times, until further orders, tomove in any direction that may be required. Should you hear very heavy firing in the directionof Harper's Ferry you willmove toward it at once with your command, and report your departure to these headquarters.

Very respectfully, &c.,

R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Camp near Urbana, September 12, 1862-6.15 p. M.

Major General A. E. BURNSIDE.

Commanding Corps, &c.:

GENERAL: The commanding general directs that you move to-morrow morning at daylight and mass your troops at Frederick, leaving one brigade at the Monocacy crossing. Please have a staff officer here to receive orderse at daylight to-morrow morning. Franklin moves to Buckeystown in the morning, Couch to Licksville. Porter, with his corps of 20,000 men is en route to join this army. Banks' corps to move by Ijamsville and Crum's Ford to Frederick, halting one mile this sid eof the town. Headquarters will probably be at Frederick to-morrow night.

Very respectfully, your obedient servant,
R. B. MARCY.

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Near Urbana, September 12, 1862-11 p. M.

Major-General BURNSIDE:

Frederick, Md.;

GENERAL: The general commanding directs you to ascertain if the enemy moved from Frederick by way of the National road. In case he took that direction, you will move with your command at daylight in the morning along the National road cautiosuly, and obtain possession, if possible, of the pass by which the National road passes through the Catoctin range of montains, so a to allow General Pleasont's cavalry to debouch intoteh Catoctin Valley beyond. Should you gain this pass, you will hold it for the purpose specified and report for further orders. Should you find the pass occupied by so strong a force of the enemy as to render the taking it by your command a matter of to much risk, you will report the fact at once to the commanding general at Frederick, who will send forward a sufficiency of troops to your assitsance. The general desires you to learn, if possible the condition of affairs in the direction of Harper's Ferry and to communicate the same to him. Governor Curtin telegraphs that he has advices that Jackson is crossing the Potomac at Williamsport to return into Virginia. Ascertain if this movement is being made by Jackson, and communicate with these headquarters the result of your investigations. Communcate the contents of this dispatch to Brigadier-General Pleasonton, who will co-operate with you as far as may be necessary. The staff officer who carries this will accompany you to-morrow and bring