Main force ; that Rodes, with Johnson and Jones, is about Sharpsburg, with not exceeding 8, 000 men ; that Imboden has been out into Pennsylvania, stealing horses and plundering. Ny opinion is that Ewell's whole force, which has passed beyond Winchester, does not exceed 30, 000 men, and I think that of this force but, say 12, 000 men are about and beyond Williamsport.

Dan. Tyler,

Brigadier -General .

The entire command engaged, under direction of Colonel Raynolds, in improving the defenses, and making satisfactory progress. Are greatly in want of cavalry, to obtain information from Loudoun Valley and the Shepherdstown region. June 21. - Up to this date there has been no evidence obtained here from scouts, prisoners, or deserters that any heavy body of rebels had passed the Potomac, and from the best sources of information, I doubt if over 8, 000 or 10, 000 men have passed beyond Sharpsburg, and these are foraging in Pennsylvania. In answer to a telegram from Major-General Hooker, as to the time I could hold Maryland Heights, I telegraphed as follows:

Headquarters, Maryland Heights, June 20. 1863.

(Received War Department June 20-8, 30 a. m.)

Major-General Butterfield:

If attacked by 30, 000 men, I can possibly hold out for say, three days . I shall hold out as long as I can . I am satisfied that Rodes and Johnson, of Ewell's corps, with, say, 8, 000 men, are on this side of the Potomac . I was expecting an attack last night, and have been arms since 3 o'clock, but none has been made. I begin to think we are not to be attacked.

Dan. Tyler,

Brigadier -General

About sunset, one of our scouting parties returned from the neighborhood of Sharpsburg, and gave the first positive information that a large rebel force was moving on Hagerstown and in the direction of Pennsylvania. At 10 p. m. telegraphed General Hooker as follows:

Headquarters, Maryland Heights, June 21, 1863-10p. m.

Major-General Hooker,

Commanding Army of the Potomac:

Lieutenant F. G. Martindale, of the First New York Cavalry, left the mountain between Sharpsburg and Shepherdstown Ford, at the burned mill, at 5 p. m., where he said he could see into the camps clear and sure . He says troops were passing the ford toward Sharpsburg, and he estimates the entire force at and about Sharpsburg at 20, 000 . He says he saw regiments lying in the open field, without any attempt at concealment. He saw only one battery sure, but he thinks he saw between three hundred and four hundred wagons, and also saw wagons coming into Sharpsburg at a slow gait, as if heavily loaded, from the direction of Boonsborough and Hagerstown. Saw one regiment of infantry go out on the Boonsborough road, and did not return during the six or seven hours he was examining the troops, &c., Lieutenant Martindale saw little cavalry in proportion to the infantry.

Dan. Tyler,

Brigadier -General.

The entire command to-day occupied in throwing up entrenchments and sinking rifle-pits. June 22. - Telegraphed Major -General Hooker at 2 o'clock as follows:

Headquarters Maryland Heights, June 22, 1863-2 p. m.

Major -General Hooker Commanding Army of the Potomac:

The rebel forces in and around Sharpsburg are exclusively employed collecting plunder in Pe nnsylavania and Maryland . A large train just passed the Shepherds-