Washington, July 13. The following dispateh was received tody at headrjuarteri', frora Gen. McUlellan. " Beverly, Va., July 13. " Tlic suceess to-day is all I could de8Írc. Wc. capturcd six brass cannon, of Íhioh onc is rifled, and all tho cnemy's ,mp equippagc and transportations. The numbcr oí teuts will probably reach 200, and more than CO wagons. " Their killed and wounded amount to fully onc hundred and fifty, and at least oue huudred prisoners, and more coruing in constantly. I know already of ten officers killed and prisoners. Their retreat was completo. " I oceupied Beverly by a rapid march. Garnett abandoned bis camp carly this morniug, leaving much of hts equippage. líe carne within a few miles of lieverly, but our rapid march turned him back iu great confusión, and he ia now retreating on the road to St. Gcorgo. Gen. Morris is to follow him up closely. " I have telegraphed to the two Pennsylvania regimonts at Cumberland to join Gn. Hill at Koalesburg. Tho General is concentrating all bis troops at Roalesburg, and will cut off Garnett's retreat near West Union, or if possible, at 8t George. " I may say that we have driven out some 10,000 troops strongly entrenehed with a loss of eleven killed and thirtyfive wounded. Provisión returns found here show Garnett's forcé to have been 10,500 men. They were Eastern Virginians, Georfians, Tennesseans, and I think Carolinians. To-morrow I can give full details as to prisoners, &c. ' I trust that Gen. Cox has by this time driven Governor Wisc out of the Kanawha Valley. In that case I ehall have accomplished tho object of liberating Western Virginia. " I hope tho General in chief will approve of my operations. (Signed) " G. B. McCLELLAN."