HEADQUARTERS DEFENSES OF WASHINGTON,
September 14, 1862-1.30 p. m.

Major General S. P. HEINTZELMAN, Arlington:

The General-in-Chief directs that General Stoneman proceed without delay to the Upper Potomac, with six regiments of his own division, to take command, also, of the two regiments and battery now there. He is to guard the crossings from Great Falls to Point of Rocks, having his main force at some central position, such as Poolesville, to be selected by him. General McClellan telegraphs that the affair yesterday at base of South Mountain was a complete success at all points. The enemy are in a full retreat. All the troops, new and old, he says, behaved splendidly. General Reno was killed. Please acknowledge.

RICH'D B. IRWIN,

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

WASHINGTON, September 14, 1862.

Major-General BANKS,

Commanding Defenses, &c.:

GENERAL: On examining Fort Lyon I find there is an immense quantity of work required to put it in a proper condition. It is a very large work, and requires a garrison of 1,400 men for defense, at a minimum estimate. It is now occupied by three companies of the Third New York Artillery Battalion, numbering between 300 and 400 men. They would suffice to serve the guns, though I think it would be better, as few of the guns at Fort Ellsworth have now any bearing, unless our outer line is forced, to take the fourth company of this battalion from the latter work and send it to Fort Lyon.

I think there should also be a regiment assigned to Fort Lyon as a part of its permanent garrison. I fine of the new regiments can be found, commanded by an experienced colonel, it would answer the purpose. It will probably be said that an old regiment cannot be spares. However that may be, some course should be immediately taken that will insurer a proper defense of this work if attacked.

The other works are much smaller, and if they have not their infantry garrisons in them, they are close by, and there are experienced officers in general charge, who would know how to post them. Fort Lyon is isolated. Whoever commands this work, in case of attack, must have studied it, and made himself familiar with its arrangements. As is is, it would be likely that if a force would be thrown in, in case of sudden advance of the enemy, quite unacquainted with their duties, that there would be discordance between the new commander and the present artillery commander. My duties as the engineer do not permit me to keep myself informed as to the dispositions and changes of dispositions of troops, and I can only state the necessity, without being able to say exactly how to meet it. If a regiment is sent fa Fort Lyon, I would be able from it to obtain details for the work to be done in and near it. i need 400 men, at least (a daily detail), around Fort Lyon, and an equal number for work on lines between Forts Ward and Worth, and between Forts Worth and Lyon. Hooker's old division is encamped near these works, but the commanders are very reluctant that their men should now work. There appears to be a large force of troops near Fort Ellsworth. If there is to be any stability in their position, these would furnish the necessary details. I do not wish to excite the idea of great