NASHVILLE, TENN., December 9, 1862-11 p.m.

Major-General H. W. HALLECK,

General-in-Chief:

In reply to your telegram, inquiring why the brigade was stationed at Hartsville, I respectfully state that it was necessary to cover the crossing of the Cumberland River against rebel cavalry, who would essay to attack our road and capture our trains. We have, for all our immense line of front communications, picket, and couriers, less than 4,000 cavalry, and the enemy not less than 10,000 who are much relieved by guerrilla scouts, and can concentrate for mischief with almost perfect secrecy and impunity. The subjoined copy of General Thomas' report shows that it was a pretty full brigade, posted strongly, with a cavalry regiment for picket duty on the north side of the river, in a commanding position; that it was strongly supported within 9 miles, and, but for being surprised and making feeble resistance, it would have been succored, and the enemy badly whipped. That outpost was stronger and better supported than our outpost at Rienzi, 7 miles below Corinth, last summer. The difference was in the superiority and number of rebel cavalry.

Hartsville was garrisoned by the Thirty-ninth Brigade, Twelfth Division (Dumont's), for duty, and was commanded by Colonel A. B. Moore, One hundred and fourth Illinois. There was also a regiment of cavalry posted there, the Second Indiana, sent there by your order. The effective force not known. The troops were posted so as to guard the ford and the approaches from the direction of Lebanon, and the cavalry for picket duty and scouting. Colonel J. M. Harlan, Second Brigade, First Division, was posted at Castalian Springs. This brigade reports 2,725 men present for duty. The last two brigades mentioned were 9 miles distant from Hartsville when the attack was made. As soon as cannonading was heard, Colonel Harlan ordered Colonel Miller to march with his command in the direction of Hartsville, and, with a portion of his brigade, followed Colonel Miller, and orders were given to the cavalry from these headquarters to be vigilant and scour the country, so that no enemy could approach without giving timely notice to the garrison. Colonel Harlan, upon being relieved by Colonel Scott at Hartsville, informed me that the position was strong and defensible; added to the information received from my officers, let to the belief that the officer in command allowed himself to be surprised, which resulted in the capture of nearly his whole force. The attack was sudden, and so quickly decided that it was impossible for re-enforcements to reach Hartsville in time to take part in the action, and the enemy have been defeated and probably cut off before crossing the river.

GEO. H. THOMAS,

Major-General.

W. S. ROSECRANS,

Major-General, Commanding.

WAR DEPARTMENT,

Washington, December 10, 1862.

Major-General ROSECRANS,

Nashville, Tenn.:

The most important of the President's inquiries has not been answered. What officer or officers are chargeable with the surprise at Hartsville and deserve punishment?

H. W. HALLECK,

General-in-Chief.

NASHVILLE, TENN., December 10, 1862-midnight.

Major-General H. W. HALLECK,

General-in-Chief:

Additional information from Colonel Limberg and Captain Good, One hundred and eighth Ohio Volunteer Infantry, who were present in the