...y are in Alexandria this morning, thus leaving that portion of the army of the Potomac that joined Pope without supplies of any kind. All the supply trains of Gens. Banks, Slegell McDowell, and Heintzelman , with a part of Gen. Porter's were exposed to the rebel attack at Centreville, and would undoubtedly have been captured on Wednesday night, had it not been for the heroic resistance of one company of...