render it absolutely necessary for your to put your command in motion at once to re-enforce him. It is of the utmost importance that you should reach his position before daylight. A part of General Couch's division marched to the vicinity of Williamsport last night. The night march is therefore practicable. Captain Lowell, who has just returned from there, is of the opinion that the Sharpsburg and Hagerstown pike to Jones' Cross-Roads is the best road to take. You will find some of our cavalry at the cross-roads, who can inform [you] of General Couch's position. You will please assume command of all the troops in that vicinity, and endeavor to defeat and capture the rebel troops opposed to you. In addition to Couch's division, you will have under your command three brigades of Pleasonton's cavalry, three horse batteries, and a brigade of infantry from Hagerstown. It would be well for you to communicate with General Couch at once by a special messenger, informing him as to the probable time of your arrival.

Very respectfully, yours,

R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC,
Centerville, September 20, 1862--10.15 a. m.

Major General D. N. COUCH:

GENERAL: Your communication of 8.40 a. m. to-day is received. The commanding general directs me to say that he wishes you to occupy the town of Williamsport, if you can do it without risk, and to ascertain as definitely as you can what force of the enemy is in the vicinity. The ford should certainly be held to prevent passage by them, and it might even be well to threaten it yourself, as you suggest. This must be left to your judgment. General Pleasonton has probably joined you by this time.

Yours, very respectfully,

R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC,
Near Sharpsburg, September 20, 1862--7.15 p. m.

Major-General COUCH:

GENERAL: Franklin is ordered to send you one division. Pleasonton is also directed to send you one brigade of cavalry and one horse battery. General Kenly, with the Maryland Brigade, is also ordered to join you from near Hagerstown. All these troops will be with you before daylight.

I am, general, very respectfully, your obedient servant,

R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC,
Near Sharpsburg, September 20, 1862--8.30 p. m.

Major-General BURNSIDE:

General McClellan directs me to say that the force of the enemy in front of General Porter seems merely intended to cover retreat of wagon train, &c. There is some force of the enemy at Williamsport, against which Couch moved this morning, and Franklin is ordered to go to-night. Williams' (Banks') corps arrived at Maryland Heights at