BRILLIANT AFFAIR IN KING AND QUEEN COUNTY-COLONEL DAHLGREN KILLED.

News was brought in during the morning of the brilliant affair of a small body of Confederate cavalry under the command of Lieutenant Pollard, who had attacked a body of yankee cavalry under the command of Colonel Dahlgren, killing their commander, taking 90 prisoners and 35 negroes and 150 horses. The fight occurred at Walkerton on Wednesday night about 11 o'clock. The body of cavalry under Dahlgren's command numbered some 300 or 400, being part of the force which had appeared on the Westham plank road. They had crossed the mattapony at Aylett's. The wretch who commanded them was the son of Commodore Dahlgren, of ordnance notoriety. It would have been well if the body of the land pirate had been gibbeted in chains on the spot where he fell. Lieutenant Pollard commands Company H, of the Ninth Virginia Cavalry. He was aided by some home guards and a small detachment from Lieutenant-Colonel Robins' command.

From the courier who came in yesterday we have some interesting particulars of Lieutenant Pollard's affair with the enemy. It appears that with his company of cavalry he followed the enemy across the Mattapony during the whole of Wednesday, harassing his rear. At the forks of the road the enemy took that leading to Walkerton, while Lieutenant Pollard, directing a few of his men to follow the enemy on that route and make a pretense of pursuit, rapidly withdrew the large portion of his force to the other road. He succeeded in making a circuit of the enemy, and about 11 o'clock at night appeared on their front, having been joined by some home guards and a few of Robins' command. The Yankees attempted to charge through our lines, the charge being headed by Dahlgren himself. He was shot dead before his column came in contact with our lines. A fight ensued, with the results referred to, to which we may add the fortunate circumstance that not a man of our command was killed. Several Yankees were killed, and the force not captured was dispersed in a wild flight, aided by the cover of the woods and the night.

FULL DISCLOSURE OF THE ENEMY'S PLANS-RICHMOND TO BE DESTROYED-THE PRESIDENT AND HIS CABINET TO BE KILLED, ETC.

The following papers and memoranda were found on Dahlgren's person, and contain the indisputable evidence of the diabolical designs of the enemy.

The following address to the officers and men of the command was written on a sheet of paper having in printed letters on the upper corner, "Headquarters Third Division, Cavalry Corps, ---, 1864:"

OFFICERS AND MEN:

You have been selected from brigades and regiments as a picked command to attempt a desperate undertaking-an undertaking which, if successful, will write your names on the hearts of your countrymen in letters that can never be erased, and which will cause the prayers of our fellow-soldiers now confined in loathsome prisons to follow you and yours wherever you may go. We hope to release the prisoners from Belle Island first, and having seen them fairly started, we will cross the James River into Richmond, destroying the bridges after us and exhorting the released prisoners to destroy and burn the hateful city; and do not allow the rebel leader Davis and his traitorous crew to escape. The prisoners must render great assistance, as you cannot leave your ranks too far or become too much scattered, or