Afternoon Report.

15,000 Rebels on the Maryland side.
Jackson's Force 45,000
Rebel Steamer Nashville Burned Near Savannah.
From Washington.

WASHINGTON, Sunday — 11 P.M.

The following account has just been received from the Potomac. It is believed to be reliable:

The rebel force in the neighborhood of Dorrestown and Clarksburg, is estimated at 35,000, and is composed entirely of cavalry. A body of the enemy, about 1,500 strong, crossed the river last night at White's Ferry, and are supposed to be en route to Frederick. — Our forces hold the bridge across Seneca Creek, which was not injured by the rebels on their return from the recent dash on Dorrestown. It has been ascertained that Jackson crossed the Potomac opposite the bank of the Monacy, and passed along the bank of the stream to Frederick. A rebel picket, captured near Clarksburg to-day, says Jackson's force is 45,000.

Hon. Henry Love and Garrett, of Illinois, are here to obtain certain charges in the management of the war in the west.

Advices from Gainsville, which is about two and a half miles beyond Bull Run, state that the rebels attacked our forces yesterday with the 35,000 from Richmond. A division under Gen. Walker has left Gainesville for Leesburg. My informant say Jackson, Longstreet and Hill at Gainesville, and counted forty-four pieces of artillery, mostly rifled guns. None were larger than 12-pounders. At Centreville he saw a few cavalry only, and a batter which was returning from having, as they said, driven the Yankees away from Munson's Hill.

One of the Times correspondents left the vicinity of Fairfax C. H. about 4 o'clock this morning. Our pickets are within 4 miles of that place. The enemy's pickets seem to be within about a mile of Fairfax, in a semi-circle in a space on the Southwest. There was been no new action.