Washington, July 15. An official dispatch has been recoivcd nt head quarters from Gen. McClellan,ÍVo:n Huttonsvillo, Va., I5th, giving an account of the routing of the forpes and de:ith of (jen. Garnett.oonfirttlisg the previoii8 account. Ilesavshc ha- completely annihilated theeneniyin Western Virginia, " Our loss is but thirteen killed and about fortv wounded. The enemy's 200 killed and"l,000 prisoners. We captured seven guns. "A poi'tion of Garnett's forco retreated, but I look for them captured by Gen. Uil!, who is in hot pursuit. "It is said that Garnett's troops are the crack regimenté of Eaptern Virginia, aided by Georgian?, Tennesseans and Caroliniane. Our suoeess ia complete, and I firrnly believe thrit secession is killed in this section of the country. Grafton, Va. July 15. A train arrived hero thia morning bringing tho body of General Garnett, late commander of the rebel forces in Western Virginia. Tlie rebels were pursued from Laurel Hill by Gen. Morris' command, consisting of tho Fourteenth Ohio and Seventh and Ninth Indiana Koginients at Carrick's Ford. - Eight miles south of tho town of St. George, Gen. Garnett attempted to rally his forces, when a shurp skirmish ensued, in which Garnett wae killed and twenty of his men werb left dead on the giound, besides many bodies being carried off. Tbc rebels were cornf letely routed and cattered in all direclions, and foity loaded wagons and all thcir horses and camp equipage feil into ouv hands. Gen. Garnett's remains will be embalined and placed at the disposal of his friends. Tiro men were killed and two mortally wounded of tho Ohio Fourteenth. There was uo other loss on our side. Our troops took moro prisoners than they oould take caro of.