HEADQUARTERS DEPARTMENT OF THE POTOMAC,
Arlington, September 12, 1862.

General BIRNEY, Commanding, Seminary:

General Grover is ordered to relieve you, but you will move without waiting for his troops, leaving a staff officer to point out to him the ground now occupied by you. You will please assume command of all troops within your lines, except the garrisons of the forts. There is a cavalry brigade near Fort Blenker. Please direct the commanding officer to send three mounted orderlies to report to General Slough, military governor of Alexandria.

CHAUNCEY McKEEVER,

Chief of Staff.

ALEXANDRIA, VA., September 12, 1862.

ASSISTANT ADJUTANT-GENERAL,

General Halleck's Headquarters:

I have received no order from any source to retain any portion of the troops outside of Alexandria, lately under my command. General Grover consents that I may use the Thirty-third Massachusetts for a short time, and until I can have assigned me other troops. Will you please send me a regiment, for, without one, Alexandria will soon be in the control of drunken stragglers, as I have not force enough without to prevent.

JNumbers P. SLOUGH.

Brigadier-General.

WASHINGTON, D. C., September 12, 1862.

General McCLELLAN:

The following is a copy of Associated Press report, dated Baltimore, 12th:

Last evening, at 7.30 o'clock, the rebels made a cavalry raid into Westminster, about 500, with two pieces of artillery. As they charged through the village, discharged their pistols on unarmed citizens on the street. C. W. Willister, district attorney, seeing rebels coming, made for the railroad, and, after proceeding about 1 mile, met train from Baltimore, which, on his information, returned immediately. There was at Union Bridge a train of the Western Maryland Railroad (locomotive and two cars), which should have arrived at Westminster at 5 o'clock this morning, and in this city at 8 o'clock. This train has probably been captured. Federals occupied New Market, on Baltimore and Ohio Railroad, 10 miles from Frederick, yesterday.

STAGER.

BALTIMORE, MD.,

September 12, 1862-2.30 p. m.

General HALLECK, General-in-Chief:

You can put any of my troops under McClellan's command. They are all on the railroad, in detachments and regiments. I have two regiments at the Relay House, one at Ellicott's Mills, one at Elysville, perhaps 7,000 or 8,000 at Harper's Ferry, and two regiments and a battery at Martinsburg. They may abe in his neighborhood, and you can give him authority to use them as you or he may deem proper. I have no available troops except those posted on different railroads.

JOHN E. WOOL,

Major-General.