FEBRUARY 9-10, 1864.-Expedition from Fernandina up Nassau River, Fla.

Report of Captain De Witt C. Lewis, Ninety-seventh Pennsylvania Infantry.

FERNANDINA, FLA., February 11, 1864.

SIR: I have the honor to make the following report of an expedition up Nassau River, of which a detachment of the Ninety-seventh Regiment Pennsylvania Volunteers under my command formed a part:

We embarked and sailed from this place at 10.30 a.m. for Nassau, by the way of Amelia River, February 9, accompanied by detachments of sailors from U. S. brig of war Perry and gun-boat Para, commanded by Lieutenant Hanford, of the U. S. Navy. At Station bridge, on the railroad, we discovered a party of the enemy, consisting of 3 mounted men, who were driven out of sight by the firing of a shell at them. At 2.30 p.m., we entered Nassau River, and proceeded up that stream to Nassau Mills, some 25 or 30 miles, meeting on our way but two posts of the enemy's pickets, who retired on our approaching them. One was stationed at Cooper's Bluff and the other at the Jacksonville road. We arrived at the miles about 5 o'clock in the afternoon, shelling the woods on our way up on both sides of the river, and were met at the mills by two ladies with a flag of truce, who reported themselves as being the only persons on the island at the time, one of them being the wife of a gentleman by the name of Holmes, the owner of a large steam saw-mill that was in the course of erection at the commencement of the war. We sent a boat and took them on board as a precaution against treachery, and again moved up the river some 4 miles farther, taking the distance by the channel of the river, which is very crooked, and came to anchor about 8 o'clock in the evening, the night being very dark. We immediately threw out pickets some 300 yards in advance of the vessel. As soon as the tide commenced running out a large amount of timber floated down, supposed to have been cut loose above by the enemy for the purpose of injuring the steamer, as a number of signal lights were seen on each side of the river above the vessel.

At daylight on the morning of the 10th, the anchor was hoisted and we dropped down below the new mill about half a mile and landed the ladies. At 10.30 the detachment of the Ninety-seventh Pennsylvania Volunteers, commanded by Captain Savage, appeared in sight, some 2 miles from us across the marsh; sent a board to communicate with them and bring them on board. In the meanwhile had the boat run close inshore and landed to examine the condition of saw-mill; found the old one in bad order, but the new one nearly ready for running, with an engine of some 50-horse power, with five tubular boilers, set furnaces, and everything complete except steam connections between engine and boilers. The gearing of the mill appears to be complete with exception of belting, a part of which is there. There are two sets of frames for gang and two for circular saws. The ways for drawing logs on the mill are laid, and the gearing for that purpose appears to be ready for use. I think timber can be sawed 60 feet in length, and there is a large quantity of it in the water before and above the mill. All the sawed lumber has been destroyed by the enemy. The old mill is some 300 yards above the new one. We found in the channel of the river about 2 fathoms