Ferry is confirmed, push on with your whole command (cautiously and keeping up communication with Franklin [Burnside]) to Sharpshburg, and endeavor to fall upon the enemy and to cut off his retreat. Use your cavalry with the utmost vigor in following up the pursuit. In this juncture much is left by the commanding general to your judgment, trusting that you will act promptly and vigorously and complete the success thus far gained.

By command of Major-General McClellan:

GEO. D. RUGGLES.

Colonel and Aide-de-Camp.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

September 15, 1862-1.20 p. M.

Major-General FRANKLIN.

GENERAL: Burnside's corps and Sykes' division are moving on Porterstown and Sharpsburg by the road about one mile south of Hagerstown pike, with orders to turn and attack a force of the enemy supposed to be at Centerville. I will instruct them to communicate with you at Rohrersville, and if necessary re-enforce you. It is important to drive in the enemy in your front, but be cautious in doing it until you have some idea of his force. The corps of Sumner, Hooker, and Banks are moving to Boonsborough on the main pike. At least one division has already passed down toward Centerville. I will direct a portion to turn to the left at the first road beyond the mountain (west), so as to be in position to re-enforce you or to move on Portersville. Sykes will be at the Boonsborough and Rohrersville road in about one hour and a half, Burnside following close. Thus far our success is complete, but let us follow it up closely, but warily. Attack whenever you see a fair chance of success. Lose no time in communicating with Sykes and Burnside.

Very respectfully, your obedient servant,
GEO. B. McCLELLAN,

Major-General.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Boonsborough, September 15, 1862-4.30 p. M.

Major General W. B. FRANKLIN, Commanding Sixth Corps:

GENERAL: The commanding general directs me to say to you that he is now in a position to cover your rear, and you had better withdraw the two brigades left at Rohrersville and order them [to] join you, doing your best to hold your position without attacking unless you should see a very favorable opportunity. It is his desire to concentrate everything this evening on the force at or near Sharpsburg, and he will be satisfied if you keep the enemy in your front without anything decisive until the Sharpsburg affair is settled, when he will at once move troops directly to your assistance and also to endeavor to cut off the enemy in front.

Yours, very respectfully,
R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Bolivar, September 15, 1862-8 a. M.

Major-General BURNSIDE, Bolivar:

The general commanding directs you to advance with your whole corps upon Boonsborough by the road which you followed yesterday,