comparison with the ruin and disaster which would follow a signal defeat of this army. If we should be successful in conquering the gigantic rebel army before us, we would have no difficulty in recovering it. On the other hand, should their force prove sufficiently powerful to defeat us, would all the forces now around Washington be sufficient to prevent such a victorious army from carrying the works on this side of the Potomac, after they are uncovered by our army? I thin not.

From the moment the rebels commenced the policy of concentrating their forces, and with their large masses of troops operating against our scattered forces, they have been successful. They are undoubtedly pursuing the same now, and are prepared to take advantage of any division of our troops in future. I, therefore, most respectfully, but strenuously, urge upon you the absolute necessity, at this critical juncture, of uniting all our disposable forces. Every other consideration should yield to this, and if we defeat the army now arrayed before us, the rebellion is crushed, for I do not believe they can organize another army. But if we should be so unfortunate as to meet with defeat, our country is at their mercy.

Very respectfully, your obedient servant,

GEO. B. McCLELLAN,

Major-General.

WASHINGTON, D. C.,

September 11, 1862-p p. m.

Major-General McCLELLAN, Rockville, Md.:

General Fitz John Porter's corps has been ordered to move to-morrow to Brookville, via Leesborough, to report to you for duty in the field.

H. W. HALLECK,

General-in-Chief.

HEADQUARTERS ARMY OF THE POTOMAC,
September 11, 1862-11.30 p. m.

(Received 3.40 a. m., September 12.)

Major-General HALLECK,

General-in-Chief:

GENERAL: My signals have to-day been established on Sugar Loaf Mountain. At last advices, Burnside's troops were within 2 miles of New Market. I have ordered him to advance to-morrow, if possible, to Frederick and occupy it; Sumner and Franklin to advance early in the morning to Urbana, Couch following the movement, after leaving a force to guard the fords below the Monocacy. I am much obliged to you for sending me Porter's corps, and should like the remainder of Keye's corps as soon as possible. I shall follow up the rebels as rapidly as possible.

GEO. B. McCLALLAN,

Major-General, Commanding.

ROCKVILLE, [MD.],

[September] 11, 1862-1 p. m.

General AMBROSE E. BURNSIDE, Brookville:

The commanding general will not move Sumner and Franklin on Urbana until he hears from you, after your movement toward New Market is decided. Should you think that the taking that place will be likely to bring on a general engagement, you will not make the attack. This you can probably judge of after your reconnaissance this morning.

R. B. MARCY.