The major-general commanding directs me to say that Captain McKee will get orders to-morrow for his work. You are, are this, probably advised that General Slocum is at Leesburg. This will save you detaching any force to hold that place. It is expected that we shall have telegraphic communication with headquarters, via Poolesville, from Leesburg, to-morrow a. m. ; also that telegraphic communication will be open from headquarters to General Reynold's corps, stationed on the Leesburg and Alexandria Railroad, between Guilford and Herndon Stations, at Kipp's and Brady's Mills. The general says your orders are to find out where the enemy is, if you have to lose men to do it. Your prisoners have arrived here. Slocum's orders require him to hold Leesburg and the fords in that vicinity. This leaves no opportunity for any cavalry of the enemy to cross at these fords from Maryland. Stahel's reconnaissance-two regiments, about 800-left Centreville early this morning for Warrenton, Sulphur Springs, Rappahannock Station, &c., to see what is there, and inform you of anything of note. Have shown your dispatch to General Ingalls with regard to young horses breaking down. Your dispatch of 1. 15 p. m. concerning Colonel Duffie being surrounded has not arrived. The general trusts that this is not true. Headquarters at Fairfax Court-House.

Very respectfully, &c.,

DANL. BUTTERFIELD,

Major-General, Chief of Staff.

ENGINEER DEPOT, Near Narry-Yard, Washington, D. C.,

June 18, 1863-8 a. m.

General S. WILLIAMS,

Assistant Adjutant-General,

Army of the Potomac:

SIR: I have the honor to make the following brief report of my operations since the receipt of the order to make up the bridges on the Rappahannock on the 13th instant: I was down at the crossing with my men and teams about 9 p. m., when I had been notified all would be across. The crossing commenced, however, only at about 10 p. m., and, at about 11. 10, I was notified by General Newton that one bridge could be taken up, and, at about 12. 10, that the second could be removed. The troops, however, continued to straggle down for nearly three hours after, and boats sent over for them, although the night was a part of the time intensely dark. The two bridges were taken up, and I saw the last chesses loaded at about 4 p. m. The last pontoon was specially reported to me to be upon its truck, and every truck with its pontoon. Some delay was caused by hunting up the pontoons, as the men of the crossing force, as reported to me, had left many adrift after crossing their commands. The bridge trains closed upon our old camp about 5 a. m., and, after the necessary feeding of the teams, started at once for Aquia Creek, I myself preceding them, reaching that station about 8 a. m., in time to obtain a boat and go with the regular battalion to Occoquan, to see the bridge laid there, which was completed at about 5 p. m. of the 14th, or one hour earlier than the order required, the fact being reported through General Slocum.