FALMOUTH, VA., August 27, 1862 - 10 a. m.

(Received 10.40 a. m.)

General HALLECK, General-in-Chief:

I have just received the following from General Porter:

ADVANCE, 26 - 11.45 p. m.

General BURNSIDE, Falmouth:

Have just received orders from General Pope to move Sykes to-morrow to within 2 miles of Warrenton and to call up more to same point, leaving the fords guarded by cavalry. He says the troops in rear should be brought up as rapidly as possible, leaving only a small rear guard at Rappahannock Station, and that he cannot see how a general engagement can be put off more than a day or two. I shall move up as ordered, but the want of grain and the necessity of receiving a supply of subsistence will cause some delay. Please hasten back the wagons sent down and inform General McClellan, that I may know that I am doing right. Banks is at Fayetteville; McDowell, Sigel, and Ricketts at and immediately in front of Warrenton; Reno on his right. Cox going to-morrow, Sturgis next day, and Franklin is expected - so says General Pope.

F. J. PORTER,

Major-General.

I have just received the following since from --

ADVANCE, 27th.

General BURNSIDE:

I am ordered to move direct to Warrenton Junction or to push the command at Barnett's, &c. The enemy have struck with their cavalry the railroad near Manassas. I expect to be out of reach of you, and you must keep back trains, &c. If you can, push up ambulances. I was them much. Your animals will have to rely on grazing. There is no grain.

F. J. PORTER,

Major-General.

Also following from Aquia Creek, which shows state of affairs there:

General BURNSIDE:

The Meager brigade is just embarking in the cars. They will leave a few minutes. They kept the two trains waiting since daylight. I reported the fact to General Sumner, who has sent his adjutant-general to inquire into the case. We have loaded about 1,100 men this morning. There are several thousand --- the river, and General Sedqwick informs me that all of General Sumner's corps will be here to-day. The Meagher brigade is now off.

H. BIGGS,

Assistant Quartermaster.

The following is my answer:

General PORTER, Advance, Va.:

Your dispatch of 11.45 p. m. just received. Forty wagons and 50 head of beef cattle have left here for Morell, and will reach Barnett's this afternoon. I have telegraphed to Captain Spear to meet them and attend to the distribution. Morell's wagons are here for ammunition and forage. They will be forwarded as soon as loaded. General McClellan has gone to Alexandria, but I am sure your course meets with his approval. Push on to re-enforce Pope as rapidly as possible, leaving what you think sufficient guards at the fords. I will send troops as rapidly as possible to the fords to relieve those you may have. Meagher's brigade is now on the road from Aquia, and the whole of Sumner's will probably be here to-morrow or next day. All quiet here.

A. E. BURNSIDE,

Major-General.

FALMOUTH, VA., August 27, 1862 - 10.20 a. m.

General HALLECK, General-in-Chief:

The telegraph is now within 7 or 8 miles of Bealeton. I am sending