Captain Best has six pieces, but two of them are non-effective, for want of men. His pieces are smooth bore and, therefore, not so good for preventing a passage over a river of such width as the Potomac. Besides, the guns of the enemy are rifled, and by their long range our smooth-bore guns could be easily driven from the banks of the river or their long range our smooth-bore guns could be easily driven from the banks of the river or their vicinity. After to-day we shall have but two companies of cavalry, and they irregular. It is not possible for this command, called upon to prevent an enemy from crossing the Potomac for a distance of over 50 miles, to do so in its present condition. The enemy can easily cross, and even have time to erect breastworks and batteries to cover his passage in any force he may wish, before we could even fire a gun against him from the main body of the division. The nearest point of the Potomac from this position is about 4 miles. It would take us at least an hour and a half to reach that point in force sufficient to oppose a passage with any hopes of success. Should we immediately send our artillery and cavalry, from the nature of the country, wooded and hilly, it would only be to lose them. The fords and ferries in our vicinity are from 8 to 15 miles distant, and the same reasons would hold with much more force.

Very respectfully, your obedient servant,

ROBT. WILLIAMS,

Assistant Adjutant-General.

LOWER MARLBOROUGH, MD., September 12, 1861.

General HOOKER, Commanding, &c.:

GENERAL: Yesterday we proceed down their rive towards Lower marlborough. After proceeding 5 or 6 miles and finding everything quiet I had determined to return to Upper Marlborough. I was met by a lieutenant belonging to Colonel Dwight's regiment, of Sickles' brigade. He showed me his instructions, which were from Colonel Dwight, directing the lieutenant to find the regiment belonging to Hooker's brigade, and to inform the colonel commanding that regiment that he, with his command, was expected to form a junction with Colonel Dwight at Lower marlborough. I accordingly proceeded to a spot near Lower Marlborough and encamped for the night. This morning subsequent to seeding my courier to you, I received from Colonel Dwight a dispatch of which the following is a copy:

SEPTEMBER 12-4 p. m.

Colonel COWDIN:

COLONEL: I shall proceed towards Benedict by an easy march. I shall reach there to-morrow. At Prince Fredericktown there is a company of cavalry, and each house known to contain a member will have to be searched. I hope to see you in my vicinity, near Port Tobacco, by Saturday noon.

Very respectfully,

WM. DWIGHT,

Commanding.

I addressed him a communication, of which the following is a copy, directing it to Colonel William Dwight, jr., commanding on west side of Patuxent River:

HEADQUARTERS FIRST REGIMENT MASSACHUSETTS VOLUNTEERS,
Lower Marlborough, Md., September 12, 1861.

Colonel WILLIAM DWIGHT:

COLONEL: I propose to proceed back from this place to a point which will enable me to march either north or south, where I shall await instructions from General