HeADQITAkTERS MlODLB DliFARTMENT, Haiü-er's Febry, Ang. 8-4:40 P. JI, J To Maj.-Gen. II. W. Hal'eok : Chiuf of Staff, Brig. Gou. Kelley reports that a suotit has jiist arrived at New Creek and reports' tint Gen. Averill overtook llie er.emy near Morelield, yesterdiiy, nnd atlacked, capturiDg nli of bis rtil!ei:y and bOO prisonors.- Nothinsr oflicial lias betn reeeived froin Gen. Avurill, iiowovei1. (Signed) P. II. SHERIDAN. Maj.Gen ComniandiDo. E. M; STAXTON, Sec. of War. JNew York, Aug. 10. The Tribune special at Harper's Ferry gives more partioulara of Averill's vioUry. Gon. Averil! attaeked the conibined forcea of McCausIand, Johnson, Gülmoro and MoNeil, on the mor uing ofihe 7th, and after a spirited h'ght, cnmpletely routed thcir cntire coiuiiiand, capturinfi nll thi ir urtillery pieces, a vast quantity of sniall stores, 400 horses and eijuipments and 4Ü0 prisoners, ir.ciuding six ti!d and 32 couipany officers. Gen. McCausIand, with liis demoraüzed command, fled to the mountains. Oar loss ivas comparatively small, being seven killed and two wouuded. Amongt our killed was Majc.r Congress ard l.st Lieut. Clark, 3d Virginia Cavalry. Thoy were struck down whilo gallantly loading u charge. Capt. Kerr was severely wounded w hile penetrating the enemy's lines.