Numbers 10. Report of Colonel Samuel P. Spear, Eleventh Pennsylvania Cavalry.

YORKTOWN, VA., July 10, 1863.

SIR: I have the honor to submit the following report of the part taken by the cavalry forces under my command in a reconnaissance lately made to the South Anna River, at the crossing of the Richmond and Fredericksburg Railroad bridge, as follows: In obedience to circular, dated White House, VA., June 30, 1863, I left camp on the 1st day of July, 1863, in command of my own regiment and five small companies of the Second Massachusetts Cavalry, in all about 1, 200 men, and proceeded as the advance guard of General Getty`s column to King William Court-House. At this point, I found a small cavalry picket of the enemy, charged him, and captured 2 men and horses, also a quantity of small-arms. The arms I destroyed, and sent prisoners to the rear. Continuing my course, I captured at the Brandywine 2 Confederate detectives of the Richmond police force. These, with papers, orders, horses, &tc., I also sent under guard, to report to the commanding general. At this point I encamped. On the 2d, I led the advance to Taylorsville, destroying five ferryboats on the river and charging and taking prisoners, Lieutenant _, commissary, and 7 privates. These were also sent to the rear. At this point the ferry-boat at Taylorsville was destroyed, and the bridge at Widow Nelson`s. This bridge was about 70 yards long, and well built; it was burned to the water`s edge. On the morning of the 4th, I was ordered to take the advance to Hanover Court-House, and thence to the Richmond and Fredericksburg crossing, or railroad bridge, on the South Anna, and "report to Brigadier General R. S. Foster. " I advanced, and found, every 2 or 3 miles, picket stations. I charged and drove them in at every one. About 6 p. m. I arrived at the destined point, and found the railroad bridge well guarded. I also found, about 400 yards above, a county bridge (so called), a wooden structure. I immediately sent to the rear, and found General Foster had not come up. I therefore advanced, and when within 100 yards of the bridge, in company with Captain P. A. Davis, of the Seventh Massachusetts Battery, I was fired upon by musketry and artillery (a 12-pounder howitzer). I immediately halted, placed my cavalry in position, and got Davis` battery together, and was in the act of placing it in position in an adjoining field when General Foster rode up, took command, and changed the position selected by me for the battery. General Foster then being in command, and I having reported to him, I acted under his orders till I returned to the White House, July 7, when I reported in person to General Getty. I will here state that the railroad bridge was of wooden trestle-work, about 100 yards long, and in the center about 70 feet high. The guns used were three in number, one a 12-pounder howitzer, one an 18-pounder howitzer, and the third a 10-pounder Parrott gun. I only judge this by sound and ammunition used. Had not General Foster came up as he did, I should have opened fire in ten minutes. Trusting my report may be favorably received,

I remain, very respectfully, your obedient servant,

S. P. SPEAR,

Colonel Eleventh Pennsylvania Cavalry.

Captain HAZARD STEVENS, Assistant Adjutant-General.