WASHINGTON, D. C.,

September 22, 1862 - 11 a. m.

Major General GEORGE B. MCCLELLAN,

Camp near Sharpsburg, Md.:

By last returns there were eight companies at Cumberland, thirty at Dry [New] Creek, and one at Romney. There were also several companies at Beverly and south, but it is believed that they have been drawn in by General Kelley.

H. W. HALLECK,

General-in-Chief.

QUARTERMASTER-GENERAL'S OFFICE,

Washington City, September 22, 1862 - 12.55 p. m.

Lieutenant Colonel R. INGALLS,

Chief Quartermaster and Aide-de-Camp,

Hdqrs. Army of the Potomac, near Sharpsburg, Md.:

Yesterday's dispatch received last night. While the right bank of the Potomac is occupied by rebels, the canal cannot be repaired or used. It is generally under artillery fire.

The railroad bridge at Monocacy is replaced, and the road can be made passable to Point of Rocks, and, if protected, to Harper's Ferry.

Stores accumulate at Monocacy and Frederick, and apprehensions are felt for their safety. The country roads between Frederick and Washington offer rare temptations to cavalry and infantry raids. The river is reported fordable in twenty places, and is not sufficiently guarded. Take care of your communications and lines of supply.

M. C. MEIGS,

Quartermaster-General.

MCCLELLAN'S HEADQUARTERS,

Near the Potomac, September 22, 1862 - 12 noon.

(Received 7.30 p. m.)

Major-General HALLECK,

General-in-Chief:

When I was assigned to the command of this army in Washington, it was suffering under the disheartening influence of defeat. It had been greatly reduced by casualties in General Pope's campaign, and its efficiency had been much impaired. The sanguinary battles fought by these troops at South Mountain and Antietam Creek have resulted in a loss to us of 10 general officers and many regimental and company officers, besides a large number of enlisted men. The army corps have been badly cut up and scattered by the overwhelming numbers brought against them in the battle of the 17th instant, and the entire army had been greatly exhausted by unavoidable overwork, hunger, and want of sleep and rest. When the enemy recrossed the Potomac the means of transportation at my disposal was inadequate to furnish a single day's supply of subsistence in advance. Under these circumstances I did not feel authorized to cross the river in pursuit of the retreating enemy, and thereby place that stream-which is liable at any time to rise above a fording stage-between this army and its base of supply. As soon as the exigencies of the service will admit of it, this army should be reorganized. It is absolutely necessary, to secure its efficiency, that the old