that Hampton crossed the river yesterday and was then at Elk Run; that he had infantry and 5 wagons. My scout returned from Elk Run fifteen or twenty minutes ago, and reported that he was there about 3 or 4 p.m.; saw only 1 man, a scout, of the enemy. A woman told him that no soldiers had passed through there recently, excepting three about 8 a.m. today. He examined the road and reports that the road from Kellysville to Elk Run seemed much worn and the tracks fresh; they crossed the run toward the railroad. The scouts from Warrenton Junction this morning reported that there were plenty of troops, said to be at Warrenton. With regard to these small parties of the enemy who are roaming about the country, I do not believe they can be captured, except by forces organized or disorganized. As they are in their native country, with citizen friends ready and willing to give information and with a thorough knowledge of the roads and woods, they possess so many advantages which are in a measure denied to us that we can scarcely hope to cope with them. However, I shall try to render them uneasy the next day or two. I forgot to mention that a rebel was captured beyond White Ridge, who objected to showing us the road to Morrisville across the country. I regret to say that while he was proceeding under escort to show us a person who would guide us, his saddle turned, and he was so much injured as to be unable to travel. The guide he recommended was a decrepit old man of eighty, who could not ride or walk. I have sent a scouting party to Catlett's, Greenwich, and Brentsville. They are expected in to-morrow.

Respectfully, your obedient servant,

WM. W. AVERELL,

Brigadier-General.

Lieutenant Colonel JOS. DICKINSON,

Assistant Adjutant-General.

No. 2. Report of Captain James M. Robertson, Batteries B and L, Second U. S. Artillery.

CAMP NEAR RAILROAD CROSSING, Potomac Creek, Va., December 23, 1862.

SIR: The report of Brigadier-General Averell, commanding First Cavalry Brigade, Hooker's grand division, dated the 22nd of December, 1862, having been referred to me, with the request that the general commanding the Army of the Potomac be informed why my battery failed to keep up with cavalry going at a walk, I beg leave to submit the following statement:

First. The assertion of General Averell "that Robertson's horse battery failed to keep up with cavalry going at a walk "is false in fact, although not intentionally made so by General Averell. On moving from the rendezvous, on the evening of the 21st instant, I found my battery placed in rear of the whole cavalry column. The night being dark, and knowing nothing of the roads or what particular road General Averell intended to take, I gave orders to keep the battery well closed up, and rode close to the rear of the regiment immediately preceding me. When the column was all in motion, I moved forward about 10 yards to the brow of a long and steep hill, and was halted by the cavalry stopping in front of me. I remained at a halt from five to ten