reduce it to about forty. There is only one company of infantry at this post (eighty men) and they are obliged to guard also the commissary, ordnance and quartermaster's stores. Application was made frequently for another company to be stationed, but the necessities of the service prevented it. To accommodate 300 prisoners new buildings must be erected within the fair grounds on the island opposite this city. In company with Captain Downing, assistant quartermaster, I examined these grounds, which have for the past year at times been occupied by troops, which have for the past year at times been occupied by troops, with a view to ascertain if the buildings now there could not be reconstructed for your purpose, but found them unfit. I have consulted a builder here, who has done work frequently with justice to the Government, and he estimates the cost of two buildings to quarter 300 prisoners, with sleeping and mess arrangements and board inclosure, at about $1,000. The wok to be done under the direction of the quartermaster and by special contract. The time to be occupied in building, twenty-one days. The plan proposed in the new building is to have two structures of about 100 feet or more in length with sleeping bunks on second floor and mess-room underneath, &c. If you prefer any particular plan, by sending it with specifications I can give you estimate of cost at this post. There is now a building on the grounds which will answer for a hospital. In case it should be necessary to send 200 or 300 prisoners here immediately I can procure temporary accommodations in three empty warehouses adjoining one another and near the present prison in the city. I have briefly reported as above, being anxious to make an immediate reply to your letter.

Very respectfully, your obedient servant,

JOS. DARR, Jr.,

Major and Provost-Marshal-General.

FREDERICKSBURG, July 23, 1862.

Colonel L. A. WHITELEY,

Superintendent New York Herald Correspondence, Washington:

Pursuant to an order from General Pope, Captain Chandler, of General King's staff, arrested last nigh four of the most influential citizens of Fredericksburg, Messrs. Knox, Barton, Gill and Wellford, to be held as hostages for the release of certain Union men carried for by the rebels last spring. The parties were taken from their beds late at night and sent to Washington this morning in charge of General King's aide-de-camp, Captain Benkard. There are now a large number of individuals visiting their families here on furloughs from the rebel army and plans are being arranged for their capture to-night. Day before yesterday the Third Indiana Cavalry met with the enemy several miles from here on the Richmond telegraph road, leaving 1 killed and 6 prisoners. Two companies of the Brooklyn Fourteenth and a squadron of the Harris Light Cavalry are in pursuit of the enemy.

CARPENTER.

HEADQUARTERS ARMY OF NORTHERN VIRGINIA,
July 24, 1862.

General GEORGE B. McCLELLAN, U. S. Army,

Commanding Army of the Potomac.

GENERAL: To carry out the cartel that has been agreed upon for the exchange of prisoners Mr. Robert Ould has been appointed agent