place for a pontoon bridge above the piers, where a part of our army crossed last year; it will require about 1, 150 feet of bridging. At Point of Rocks pontoons can be laid, requiring about 870 feet of bridge. From here there are rocks and islands down to near Noland's Ford, where Lee's army crossed into Maryland last year; the water was here let out of the canal. Hauling Ford is good; the approach on the Maryland side passes under the canal aqueduct over the Monocacy; it is easily defended. There are no good fords below this. Conrad's Ferry, near Leesburg, is a good place for a pontoon bridge, requiring about 600 feet. Above Edwards Ferry we can make a pontoon bridge, requiring about 700 feet. There is here an outlet lock from the canal into the river; also a bridge over the canal. The Monocacy itself is a troublesome stream to cross; high water. The main body of Lee's army did not come east of it last year. Conrad's and Edwards are contiguous to Leesburg. The crossings of Goose Creek are no material obstructions. We have bridges at Little Falls, Georgetown, and Long Bridge. Leesburg is a very important place, as the lowest fords of the Potomac are in this vicinity. It is 38 miles from Alexandria and 32 miles from Georgetown, over excellent turnpikes, meeting at Dranesville. The railroad is in working order at least from Alexandria to Vienna, and the whole line can easily be repaired. The best road for trains from Fairfax Court-House is via Flint Hill, Vienna, and Freedom Hill, or by Flint Hill, Hunter's Mills, and Henry Johnston's (Whipple's map). The old Ox road is, no doubt, good, as is almost every other road at this time. The distances will average about 30 miles. From Centreville, the best route, if the enemy permits, is the old Carolina road, via Gum Springs; distance, about 30 miles. From Manassas Station the troops might go via Centreville or via New Market and Sudley Springs; distance, about 37 miles.

Respectfully submitted.

G. K. WARREN,

Brigadier-General, and Chief Engineer.

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HEADQUARTERS ARMY OF THE POTOMAC, Fairfax Station,
June 16, 1863-6 p. m.

Generals REYNOLDS and HOWARD, Centreville:

Generals SLOCUM, Fairfax Court-House, and

General MEADE, Manassas:

The major-general commanding directs that you have your command ready to march at 3 a. m. tomorrow. Send an officer here at 8 p. m. for your orders.

Acknowledge.

DANL. BUTTERFIELD,

Major-General, Chief of Staff.

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HEADQUARTERS ARMY OF THE POTOMAC,
June 16, 1863-11. 45 p. m.

General REYNOLDS,

Centreville:

You will direct which of the two corps at Centrewille shall go via Frying Pan, old Ox road, and Farmwell Station, and notify General