ange and Alexandria Railroad, has just returned. Mr. Tuck reached Rappahannock Station yesterday evening and found that no trains were running there. He received information, however, from more than twenty different parties that rains are running to the Rapidan, and that the rebels are repairing the bridge at that place preparatory to running farther. The information is considered entirely reliable, coming as it does from so many parties who, without exception, made the same statements. A prisoner captured near Rappahannock Station, but who unfortunately escaped from the guard while near Centreville, gave information that he came up from Richmond to the Rapidan on the cars about a week since; that he saw the rebels busy there repairing the bridges, and that there were troops at the Rapidan. I inclose papers taken from him, which show him apparently to have been a clerk in the quartermaster's department on furlough. Mr. Tuck also reports that he heard from many different parties, three of whom had just come from there, that two or three companies of cavalry were at Culpeper. I would respectfully mention the conduct of Lieutenant Tuck as worthy of great praise. He has passed over a great extent of country, has been frequently surrounded by the enemy, has obtained satisfactory information, and has brought his party to camp without the loss of a man. I trust it may in some part atone for a misfortune to a former party under his charge. Another party sent out to go as far as Bristoe and south toward Thoroughfare Gap, returned this morning, having tone through the gap and on the White Plains. This party brings reliable information that Mosby has ordered all his men to meet him at Culpeper to-day. One of Mosby's men, taken and brought in, confirms this report. There is, this party reports, every indication that all able-bodied men under Mosby's control are preparing to leave for that direction. Is it not possible that these men, combined with a formidable force of light troops organized from the invading party to Maryland, design making a demonstration on this side of Washington or Alexandria?

I am, very respectfully, your obedient servant,

H. M. LAZELLE,

Colonel Sixteenth New York Cav., Commanding Brigadier

HEADQUARTERS CAVALRY CAMP,
Near Fort Buffalo, Va., July [17], 1864

Lieutenant Colonel J. H. TAYLOR,

Chief of Staff and Assistant Adjutant-General:

COLONEL: I have the honor to report the return of Sergeant Powell, Company K, Thirteenth New York Cavalry, sent out yesterday morning to reconnoiter about Leesburg, with the news that the enemy left Leesburg, abandoning the fords on Goose Creek, about 4 o'clock yesterday afternoon, passing off first in the direction of Snicker's Gap and afterward changing their march toward Ashby's Gap. The sergeant reports that our forces crossed the river and started on the pursuit yesterday evening, and that this morning at noon our advance was about seven miles beyond the city, still following the enemy's rear. The party returned by the way of Dranesville and reports all quiet there.

Very respectfully, your obedient servant,

H. M. LAZELLE,

Colonel Sixteenth New York Cav., Commanding Brigadier