Fear hundred negroes are working on “de mortifications’' as they eall them. Amusing are the nightly performances of Capt. Hurlbard’s ‘black walnut brigade” in dancing, fiddling and singing. They seem delighted with their new occupation, march in and out to the music of a drum beaten by a ; oolored. aspirant. They hare elected oolored officers who make most ludiorous efforts to drill them. Pre-Slavery, constitutional-Union-people look with horror upon this attempt to make soldiers of Cuffee and snuff danger in the air. There is an Indian mound standing in the middle of the fortifications which they have excavated for a magazine. It was reported that the contrabands had found there an antique vase, containing fabulous amounts of foreign gold 200 years old. The amount grew from one to f20,000. Gossip was on the qui vive, and the exoitement grew. The owner of the land rushed on to claim the spoils, and has been vigorously hunting up the facts. Up to the last advices, no one has been found who saw the prize, and no one, who has seen any one else whoCol. Leiser is bringing order out of the temporary disorder eaused by the late movements. He is ably assisted by Capt. Hurlbard, who is by all odds the most able Provost Marshal I have yet enoountedid