HEADQUARTERS PIATT'S BRIGADE, Near Winchester, Va., July 11, 1862.

Major-General POPE,
Commanding:

I have had to send one regiment to Front Royal, 400 to Middletown, and one section of artillery from the two regiments left here. There are four companies in Winchester, with the provost-marshal. This has so weakened my force that the work progresses slowly in the trenches.

Colonel Trimble sends me word from Middletown, which he received from a paroled prisoner, that General Robertson is up the valley with a large force. The man came to see me and made the same statement.

It is impossible to construct the trenches rapidly in the scattered condition of my force. In view of this I am satisfied that another regiment ought to be sent here immediately, besides the cavalry, who have not reported. The scattering of my forces is for the protection of the stores, which cause a failure of the desired end.

Very respectfully,

A. SANDERS PIATT,

Brigadier-General.

CAMP AT SPERRYVILLE, VA., July 11, 1862.

Colonel GEORGE D. RUGGLES,

Assistant Adjutant-General:

I have the honor to report to-day the whole of the First Corps in position at or near this place, having arrived here by the march and at the exact time directed by my order, made in pursuance of the instructions from General Sigel. This has been accomplished with troops suffering from heat, from insufficient transportation, and without forage. I think some credit is due them for exact performance under such difficulties.

General Milroy's brigade was established last evening 2 1\2 miles down the Culpeper road, and the First Division, Colonel Von Amsberg, near the village on the right, and the Third Division, General Schurz, to-day on the left. The Second Division, General Steinwehr, is in the rear, at Thornton's Gap. The rest of the small force of cavalry we have (Eighth New York and Sixth Ohio) is toward Luray. These are the dispositions as I was ordered. The baggage left at Luray and Milford without my orders has all been secured and sent back to Front Royal.

If, without failing in the execution of the orders given me, either as to time or any other particular, I have been able at the same time by my exertions to help save a large amount of public property; to get hospital accommodations for our many men falling sick; to have subsistence and forage forwarded without delay, and, if I have sought to secure early facilities for communication and transportation to Front Royal, where I was instructed that our depot was to be, I supposed I might win approbation instead of being surprised by rebuke. Hence I am not a little astonished at the contents and tone of your telegram, and that of your general commanding of yesterday, which I have just received. For some explanation of my acts I refer to copies of papers that I have sent you by mail, and I ask for the fullest and strictest inquiry into my conduct.

ROBT. C. SCHENCK,

Brigadier-General, Commanding First Army Corps.