Two Slavers Captured.
--Letters from Liberia to the 15th of December have been received. The schooner Quall, belonging to the Republic, had arrived at Monrovia from Gallinas, bringing with her two slave schooners as prizes to the Liberian Republic. The new mail steamer Seth Grosvenor, with the mails, left Monrovia on the 15th of December for Cape Palmas, where she would meet the British steamer bound home. The Seth Grosvenor was doing a good business. She was under contract to take the Methodist Conference to Since, and bring them back, and then was to take down the Baptist delegation to the Conference at Bassa or Since, and bring them back.