The rebel force in this department has been very much increased since our demonstration on John's Island. At that time Jackson's brigade of Georgia troops (veterans) were withdrawn from Johnston's army, and arrived in time to fight our men on John's Island. Since then more men have arrived in Charleston. In Savannah the veteran force is reported from 1,500 to 2,500 men, besides all the heavy batteries and six field batteries of four guns each.

The line of the railroad is now strongly guarded in anticipation of a raid, and field batteries are stationed at central points, so as to be able to reach each available landing place. The point upon which I hoped to effect a surprise with our 300 cavalry is now guarded by a battery 1,000 rebel cavalry. There are two points near Savannah that are accessible, but the operation will involve several days and nights spent in the rice fields, and this at this season will be apt to prostate the troops with fever. I am, however, determined to attack somewhere as soon as I can make the necessary preparations, which take considerable time, as it will now be necessary to go in full force whenever I make an attempt.

I inclose copies of letters received (unofficially) from our officers, prisoners in Charleston, with my reply.

The health of the command continues good.

I have the honor to be, very respectfully, your obedient servant,

J. G. FOSTER,

Major-General, Commanding.

Major General H. W. HALLECK,

Chief of Staff.

HEADQUARTERS DEPARTMENT OF THE SOUTH,
Hilton Head, S. C., August 4, 1864.

GENERAL: I have the honor to report, since the date of my last letter, that we have been able to achieve quite a little success in Florida.

Brigadier General William Birney having received instructions from me to seize the first opportunity that should occur for operating with his small force to destroy the railroad between Baldwin and Lake City, and at the same time to turn the former place, finding that the regiments of Georgia cavalry had been drawn away to guard the railroads in this vicinity against our threatened raid, collected quickly all his available force, and, moving up the river a short distance above Jacksonville, landed at the mouth of Black Creek, and pushing rapidly inland cut the Cedar Keys railroad, and following on quickly succeeded in destroying the long trestle-work over the south branch of the Saint Mary's River, on the Central Railroad. Turning then toward Baldwin, he advanced there on the rear of that place and forced the evacuation of that place, the enemy garrisoning it (consisting of the Florida reserves, both foot and cavalry, with fifteen pieces of artillery) retreating rapidly westward on the night of the 25th ultimo, and crossed the Saint Mary's River at the ferry in the Big Bend.

Our forces occupied Baldwin and its fortifications capturing arms, stores, turpentine, &c., in a considerable quantity, the amount not known; the turpentine was accidentally fired. Subsequently Camp Milton, between Baldwin and Jacksonville, was found deserted and occupied by our troops.

The destruction of the trestle-work on these railroads cut off two