The railroad and canal are not safe for a single night, and yet I cannot with anything like prudence detach a force for guarding the line unless strengthened for the purpose.

I suppose Major-General Patterson must have weighty reasons for leaving the point opposite Harper's Ferry without guard, for I feel that each night risks an immense amount of private property and wearies the loyal people, while it encourages the sympathizers of the enemy.

With two regiments more I can occupy the entire line from Georgetown to Harper's Ferry, and with three more do not that, but operate between General Johnston and General McDowell.

Very respectfully, I am, general, your most obedient servant,

CHAS. P. STONE,

Colonel Fourteenth Infantry, Commanding Expedition.

Brigadier-General MANSFIELD,

Commanding Department of Washington.

CAMP NEAR POOLESVILLE, July 1, 1861.

Orders, Numbers 109, which came to hand this morning.

The advance towards General Patterson's supposed position will commence this afternoon. I propose to occupy Point of Rocks to-night with six companies of the Ninth Regiment New York, to send forward the First Pennsylvania to-night as far as the Monocacy, which will enable the last-named regiment to join the Ninth New York fresh to-morrow forenoon. The rear will be covered by the First New Hampshire Regiment, which will, until the last moment possible, guard the fords and ferries near this place. To-morrow evening I shall hope to occupy the Maryland Heights, opposite Harper's Ferry, with the First Pennsylvania and six companies of the Ninth New York, having four companies of the Ninth New York at Point of Rocks, and the New Hampshire First and battalion of Pennsylvania Twenty-fifth at the Monocacy.

It will be with serious misgivings that I leave this horseshoe of the river unguarded, for I shall expect to learn that the enemy have crossed immediately on my leaving, and doubtless the canal will be destroyed, as well as large amounts of grain of the old and new crop. To guard as far as possible against such a result, I shall post 100 of the returning District of Columbia Volunteers at Edwards Ferry, with two days' rations, and shall send their baggage to the canal at Seneca, giving them orders to hold the ferry while their supplies last, and then fall back on the river, road, or the tow-path, to their baggage, with which they will return by canal to Washington. The force at Seneca,being composed entirely of District of Columbia Volunteers, will hold their position until the arrival of the former, and return to Washington with them.

I regret greatly the necessity which exists for leaving this village and vicinity without troops, as I have said before, and hope that these troops may be replaced before any evil results. The position and crops deserve occupation, if it be in any way practicable.

The time required to retire the volunteers carefully will give opportunity to send other troops, if it be deemed advisable.

Very respectfully, I am, colonel, your most obedient servant,

CHAS. P. STONE,

Colonel Fourteenth Infantry, Commanding Expedition.

Lieutenant Colonel E. D. TOWNSEND,

Assistant Adjutant-General, Headquarters of the Army.