HEADQUARTERS WESTERN DEPARTMENT, Bowling Green, Ky., December 21, 1861.

Honorable J. P. BENJAMIN,
Secretary of War:

SIR: The movements of the enemy indicate the design to turn my right by the turnpike road from Glasgow, through Scottsville to Gallatin and Nashville. They are concentrating in great force at Munfordville, on Green River, and at Columbia are rapidly increasing the number of their regiments.

Breckinridge's brigade, of Buckner's division, stationed on the railroad towards Munfordville, at Oakland, and Dripping Springs, will march to-morrow (22d) through Rocky Hill Village to Skegg's Creek, where the Glasgow road to Nashville crosses it, 23 miles.

General Buckner will also to-morrow march with the remainder of his division to the crossing of the Great Barrent River, and take a position on the west side of the bridge, 7 1/2 miles southwest of Skegg's Creek, passing en route through Rocky Hill Village (33 miles from this place to Skegg's Creek).

Major-General Hardee will march to-morrow with one of his brigades to the Great Barren River Bridge, leaving here on the route on the west side of the Great Barren River and passing through Scottsville (35 miles from this place to the bridge).

These movements will be completed in less than two days.

General Hindman's brigade, of Hardee's division, will continue to occupy his present position at Cave City until obliged by the superior force of the enemy to retire; he will then march through Rocky Hill Village to unite his brigade with the division. Rocky Hill is 18 miles from Cave City, which is 9 miles from Munfordville.

The Texas cavalry, under Lieutenant-Colonel Harrison (Colonel Lubbock is ill with typhoid fever at Nashville), and Phifer's battalion of cavalry cover Hindman's front.

Helm's regiment of cavalry keeps the country under observation towards Columbia from Glasgow.

Our forces of all arms, when concentrated on the Glasgow and Nashville turnpike road, will make an aggregate of 11,200 men.

The garrison I shall leave here is 4,160 men, composed of the Mississippi sixty days' men and one of Hardee's brigades, under the command of Major General R. Davis.

The day after to-morrow (23d) two Tennessee regiments from Camp Trousdale will re-enforce the garrison of this place, and on the 24th another is promised. These troops are uninstructed, but can be soon prepared for service.

The weather has been very fine for some weeks and the roads of every kind are excellent. I think a change is about to take place. It is now cold and cloudy, and snow and rain we hope will soon make the country roads very difficult to travel over, which would be greatly to our advantage. A slight rise of the Barren River would make the line of the Barren one of great strength.

I have made every effort to gain time to strengthen our defenses here and increase my force; in a few days more my force may be materially increased by the arrival of General Floyd's command and from other sources.

The enemy threaten an immediate move on Hopkinsville from Calhoun, on Green River, on the road from Owensborough to Hopkinsville; our force there is insufficient, but General Clark can, if beaten at Hop-