Gouverneur K. Warren to Major-General BIRNEY, June 16, 1863

Major-General BIRNEY, Commanding Third Corps: The following just received from headquarters Army of the Potomac : The general will give orders direct to the different corps. The corps at Manassas

will remain there until ordered elsewhere. Let a staff officer from each corps at Centreville and Manassas, fully posted as to all its affairs, report here at 6 p. m. touight and at 8 a. m. to-morrow. DANL. BUTTERFIELD, Major-General, Chief of Staff. JOHN F. REYNOLDS, Major-General, Commanding.

HEADQUARTERS ARMY OF THE Potomac, Chief Engineer’s Office, June 16, 1863—5.15 p. m. General BUTTERFIELD, Chief of Staff:

Sr: I present the following notes as the best the time affords. The records of the engineers have all been carried off by my predecessors. In making this up, I have the knowledge of Captain [*. H.] Paine, Major [W. R.] Biguing Lieutenant [W. A.] Roeling, Mr. Crounse, and my own.

At Hancock there isa ferry. At low water it is fordable.

At Green Springs, Stuart’s cavalry force made their crossing in the raid on Chambersburg last year. Williamsport is the best ford on the river ; made so by General Patterson. On the Maryland side the see approach passes under the canal aqueduct, over the Conococheague.

At the mouth of the Opequon is Forman’s Ford. Blackford’s Ford is a fine ford, just below Shepherdstown, where Lee’s army recrossed ane ne battle of Antietam ; no bridge across the canal; water was

Between Hancock and Blackford’s Ford the Potomac in its present state is fordable in several other places for infantry and cavalry, sufficiently so to turn any small force guarding the main fords.

At the dam above Harper’s Ferry we had a pontoon bridge on the 23d of May. The river is fordable at Harper’s Ferry, and we have a bridge over the Shenandoah, just above its mouth. There is an outlet lock here from the canal into the river. The river from here is full of rocks down to Berlin ; here there is a rope ferry and a good 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 ihe Monocacy ; it is easily defended. There aré 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 mah,

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.