HAGERSTOWN, MD., June 23, 1861.

Colonel E. D. TOWNSEND,

Asst. Adjt. General U. S. Army, Washington City:

COLONEL: Up to the present instant I have received from Captain J. Newton, Engineer Corps, only a report of a part of his reconnaissance of the Maryland Heights and the ground adjacent, made in compliance with the injunctions of the General-in-Chief. I hasten to give the result thus far, expecting to-morrow evening to present the whole.

Captain Newton approached the heights from this side, ascending over rough and steep roads difficult for artillery. The summit he found capable of defense of ample character by about five hundred men. The main difficulty to be overcome is the supply of water; the springs, which a week since afforded an ample supply, have become dry. He found no water within half a mile of the position selected on the heights for an entrenched camp. In Pleasant Valley, on the east, near the base of the mountain, springs are reported to abound; their character will be ascertained to-morrow. Water would have to be hauled from this valley, and he reports the ascent very difficult. In this valley I propose to place the force sustaining that on the heights. The whole command, if the location prove favorable, need not exceed two thousand five hundred men. That force would rendered the position safe; anything less would invite attack.

The following is what I have to report in relation to the enemy: Deserters from their ranks, some one or more of whom come in daily, all agree in saying the whole of the force originally at Harper's Ferry (said to have been 25,000 men) is still between Williamsport and Winchester, about 8,000 coming this sway on Friday at Martinsburg. The remainder are distributed in a semicircle, and on the route to Winchester, within four hours' march of the advance. The advance is approaching Falling Waters under the command of General Jackson, who now commands the whole. The force under Jackson controls the people of Berkeley County, whom I believe are sorely oppressed and would welcome our approach. That force has become some little encouraged from our not advancing, and may soon annoy us. If so, I shall not avoid the contest they may invite-indeed, if it meet the approval of the General-in-Chief, I would march my whole force, as soon as the battery receives harness, upon the enemy, and drive him step by step to Winchester. I believe this force can in ten days rid the adjoining porion of Virginia of its oppressors. I may be forced to this course.

My fear is that I may interfere with the general plan of the General-in-Chief and drive the enemy to the aid of the main body. They would, however, go as fugitives, to aid in its demoralization. My means of transportation are coming in rapidly.

I am, sir, very respectfully, your obedient servant,

R. PATTERSON,

Major-General, Commanding.

HEADQUARTERS DEPARTMENT OF PENNSYLVANIA, Hagerstown, Md., June 24, 1861.

Colonel LEWIS WALLACE,
Commanding, &c., Cumberland, Md.:

General Patterson orders you here, to come by the shortest route, unless you have strong reasons against coming that way, not anticipated by him.

F. J. PORTER,

Assistant Adjutant-General.