Virginia Troops Klt; from 'Williamsportto Falling Waters.Williamsport, Md., May 28.—The Confederate camp opposite this place has fallen back from the Potomac about four miles to Falling Wafers. The church at Falling Waters has been occupied as a hospital. On Mondav about two hundred Virginia troops reached Little Georgetown, seven miles above Williamsport, and have encamped there, usincr the church as barracks.