The Washington correspondent of the New York Tune conj.ectures that one of tho two naval expeditioos understood to bo preparing is destined for tho sheres of Soath Carolina, and the other for tho port of Brunswick, Georgia, One of these expeditions will probably start from Fortress Mouroe, and tho other irom New York. We infer the latter fro.-n this paragxaph in tbo New York World of Tuosday : The movement of naval vessels and of troops, in and about this city, indícate vory plaiuly that sorr.c cxpedition is on foot, probably for tho purpose of following up the Cupe Hatteras blow by othcrs, on perhaps more sensitivo portions of the southern coast. Of course, all tho preparaiions are as silently carried on as possible, and no one kuows certainly what point is threatened. Troops are being concentrated here, and ships are being prepared lor especial service. The steamship Vanderbilt has been thfiroughfy hauled, coalod, and matte neady for instant use as a transport.. The Baltic has been hauled out in the stream for tho purpose of being fitted out for transport service. The Atlantic is at the doek, and is ready at the notice of a few hours. Either of these vessels can. carry one thousand troops, with rationsand accoutroments. Many of the lightdraft gun-boats latoly launched are now held at the Navy Yard, having beeu reatly for sea Bome Üuie.