The trestle-works on the Cedar Keys and Lake City railroads have been burned beyond Baldwin, and the enemy has been forced to evacuate the strongly intrenched and stockaded positions of Baldwin and Camp Milton. Two locomotives and trains are cut off and must fall into our hands unless destroyed by the rebels. The rail transportation of blockade-run goods from the southern ports of Florida is broken up for the present, and the abundant supply of corn and cattle from the southern and middle counties of Florida, for the rebel armies, is within our control. The movement was a flank one. To get to the rear of the enemy our troops, after making a feint in Nassau County, on the north, ascended the Saint John's 25 miles to Black Creek, and this creek 4 miles to an obscure landing concealed by woods. Owing to deficiency of transportation it took three nights to land my small force.

We were not discovered until Sunday [July 24], when our advance began to cross the South Fork of Black Creek. This stream is from 10 to 16 feet deep. The bridge was a frail and floating one, made mostly of fence rails. While crossing our advance was attacked by the enemy's cavalry, acting as dismounted skirmishers. Colonel Beecher, Thirty-fifth U. S. Colored Troops, drove them off, and Captain Morton, Fourth Massachusetts Cavalry, pursued them. Three of our men were wounded in this skirmish, 1 seriously.

At 1 o'clock Monday morning all our troops were in bivouac at Whitesville. At 5, the column was on the march on the Clay Hill road toward Trail Ridge. Five miles out the rebels, commanded, it is said, by major Scott, were posted at a defile. They were quietly driven out by the colored skirmishers. Colonel Harris, Seventy-fifth Ohio Volunteer Mounted Infantry, was ordered to charge them with 50 men. This he did in gallant style, cutting down a cavalry man with his saber. The rebels fled, leaving 2 dead on the ground, 1 mortally wounded, and a number scattered through the swamps.

The North Branch of Black Creek was so much swollen by the recent heavy rains as to make it almost impassable. It was about 100 yards across, and deep enough for 30 yards to swim all except the tallest horses. After making a bridge for the infantry, and passing over by hand the ammunition, &c., the artillery, caissons, and wagon train were passed through.

During the crossing the Seventy-fifth Ohio was sent forward to destroy the two small trestles near Trail Ridge. This was done. The great trestle-work on the Lake City railroad over the South Fork of the Said Mary's had been burnt at 6 a. m. by Lieutenant-Colonel Morgan, of the Seventy-fifth Ohio Volunteers, with 100 mounted men of his own regiment and of the Fourth Massachusetts Cavalry. To effect this Lieutenant-Colonel Morgan had made a night march of over 30 miles, making the circuit of one of the enemy's camps, fording several deep streams, and capturing the trestle guard with its officer.

From Trail Ridge was pushed on by the Alachua trail to Darby's still on the Lake City railroad, 5 miles in the rear of Baldwin. The mounted force arrived and destroyed a long trestle; the infantry bivouacked some 4 miles in the rear. It was after midnight when the work at the railroad ceased. The day's work had been enormous.

During the night and at early dawn the rebels evacuated Baldwin and Camp Milton, passing northwestward over Brandy Creek and the Saint Mary's, and throwing away property in their rapid flight. They left us a quantity of forage, some muskets, a wagon-load of