An Expedition From New Orleans

St. Louis, July 19. The Union publishes an extract from a private letter dated New Orleans, 7th, wbïch says : Last night a stafl' ofiiver j told me that 15,000 men would start from tliis city and below on oeean ; ers to-day. They talie 15 .days rations i and ammunition, also that .thcrc isa, large nunibcr of add'itinual giiuboats in Lake l'onchartani, umi nine more vessels were added to tkc fleet. Sein.e tliink it is an expeditiou for the capttvre of Mobile, so as to command the Alabama 1! ver, and to establish a base of supplies for Slier man at Selma, wb.Ua others believe the troops are destined for Fortress Monroe. Tlii.s f orco 'iiuiy be designed to opérate witk Slocum's expodátiflu from Vicksburg, wtóch hasxeeently been reinforc.ed, ld is again marclüng iiito the interior of Missiesippi. llebel accounts of Slocum's expedition to Janksnn, Miss., claim that the Federal column undcr Ucn. Elliott was attacked on the juuetion of the Port Hudson and Kodncy roads on the 5th, and repulsed with great slaughter. Thefoad for milea being strewn with átmj nügroüs, lioraes, gnne, etc. Thj (JütubtJess refers to the expedition, coiisisjiiig of tUe SJarine brigade and two regiinents of negroes, whicn : man.-lied from Pvodnoy on the -4 tb, and were attacked by five brigades of rebel ' ea.valry, and one brigade of iuf'antry, and otter iigkting nearly all day the rebels were driven off. .O.a.r troops returued to their boats. Our loss was about 150 liil)pi. wittHiflfd ."inil iHipsinsf. j