HDQRS. DEPT. OF VIRGINIA, SEVENTH ARMY CORPS, Fort Monroe, Va., July -, 1863. (Received July 18)

GENERAL: On the 14th of June, I received from you the following dispatch by telegraph: Lee's army is in motion toward the Shenandoah Valley. All your available force should be concentrated to threaten Richmond by seizing and destroying their railroad bridges over the South and North Anna Rivers, and do them all the damage possible. If you cannot accomplish this, you can at least occupy a large force of the enemy. There can be no serious danger of an attack on Norfolk now. I had at the time this dispatch was received a force of about 5, 000 men moving up the Peninsula. The advance was near the left bank of the Chickahominy, above Diascund Bridge. I had also a considerable force on the Blackwater. These movements had been made to prevent the enemy from sending re-enforcements to General Lee from this department. At the same time all the transports in the department had been ordered to Aquia Creek, to remove the sick and convalescent of the Army of the Potomac, and the public property to Washington. On the 15th, I had not a single transport left. I went on the evening of the 14th to Suffolk, and ordered General Peck to have his command in readiness to move. On the 17th, transports returned, and were sent to Norfolk to receive Wistar's brigade, which had been ordered there from Suffolk. I advised you on the 18th that part of this brigade went up the York River that morning. The transports came in very slowly, and when they were all here, they were only sufficient to move Colonel Spear's regiment of cavalry from Norfolk to the White House. From my inability to move a larger force at once, General Getty's division, Terry's and Wistar's brigades, were landed at Yorktown. It was not until the 24th that I could send Colonel Spear with the Eleventh Pennsylvania Cavalry and about 200 men, mounted, of different regiments, under Lieutenant-Colonel Davis, of the Twelfth Illinois Cavalry, to destroy the Virginia Central Railroad bridge over the South Anna. He landed at the White House on the 25th, after constructing a wharf, for which I had ordered up materials from Fort Monroe. The same evening, on the return of the transports to Yorktown, I sent General Wistar with a part of his brigade and a battery of artillery to West Point. He pulled down two small buildings, built a wharf, and landed during the night. On the 26th, in the evening, I reached the White House, General Getty having arrived immediately before me, and being then engaged in landing his division. Major-General Keyes, with Gordon's division and Terry's brigade, and some other troops, amounting to about 9, 000 men, arrived at Cumberland on the same evening, and at the White House on the 27th. Brigadier-General Foster's brigade arrived on the 28th, making an aggregate force at the White House for duty of 18, 730. Brigadier-General Spinola arrived two days afterward from North Carolina with 1, 718 drafted Pennsylvania militia, whose term of service was about to expire, with directions that they be sent to Washington, if they would consent to serve until the insurgent forces were driven out of Pennsylvania and Maryland. They gave the requisite consent, and were embarked for Washington on the 7th July. On the 27th June, in the morning, Colonel Spear returned from the South Anna, having destroyed the bridge of the Virginia Central