The Rebels Try to Destroy Dam No. 6.

WILLIAMSPORT, MD., Dec. 20.—Affairs in and around this vicinity are quiet, though we expect to have an exchange of shots with the enemy at Dam No. 5 and Falling Waters. Gen. Jackson’s (rebel) battery is at the former place, including a 12-pounder rifled gun, and the enemy have been at work endeavoring to destroy tho dam there, which now seems to bo the principal object of their demonstrations. Their firing is returned by two Parrott guns belonging to Knapp’s Pennsylvania battery.