WASHINGTON, September 16, 1862.

Major General GEORGE B. MCCLELLAN:

In addition to the two new regiments and one battery sent up the river a day or two ago, I, this morning, dispatched to the same point, by direction of the General-in-Chief, Birney's brigade, of Stoneman's division, making in all about 4,000 infantry, with six guns and a squadron of cavalry; the whole under the command of General Stoneman. His orders are to guard the crossings from the Point of Rocks to Great Falls, and to be prepared to cross when required to co-operate in a movement on the other side. The cavalry, which has been pushed up toward Leesburg, is to communicate with him; General Stoneman expected to reach Poolesville to-night. I had intended to push a division out to Fairfax Court-House and Fairfax Station this morning, but finding that this movement, connected with the movements up the river on this side, directed by the General-in-Chief, would break the lines of defense, and considering that the surrender which we feared had taken place at Harper's Ferry might change the complexion of affairs on both sides, I thought it better to defer any advance of our lines from here until the arrangement should be more complete, and until we might be fully informed of the situation. In this view General Halleck concurred. All the troops on the other side, except the garrisons, are ordered to be ready at a moment's notice. Casey's provisional brigades, consisting of eight new regiments and two batteries, were concentrated beyond Fort Albany this morning. The dispatches received from you yesterday gave great satisfaction to the President and the Department. I shall be glad to know your views in regard to the movement suggested above.

N. P. BANKS,

Major-General.

HEADQUARTERS DEFENSES OF WASHINGTON,
Washington, September 16, 1862 - 11.45 a. m.

Brigadier General J. P. SLOUGH, Alexandria:

General Banks directs that you take immediate measures to correct the evil represented in the following communication from the General-in-Chief:

Several times the commissary store-room at Alexandria has been taken possession of by stragglers. General Slough was directed to detail a company for its protection. It appears I have been relieved, and the stragglers have again assumed control. The General-in-Chief desires the evil remedied.

Please acknowledge.

RICH'D B. IRWIN,

Captain, Aide-de-Camp, and Actg. Adjt. General

HEADQUARTERS DEFENSES OF WASHINGTON,
September 16, 1862 - 4 p. m.

Major General S. P. HEINTZELMAN, Arlington:

Casey's troops, being on the other side of the river, are certainly under your orders, but it was directed that the organization of General Casey's command should not be disturbed, as would be done by the assignment of one of its brigades to another division. The exigency of the occasion