The Potomac.
The heavy firing heard in the direction of the Potomac on Friday last proceeded from the Maryland side of the river. The Federals engaged in some ordnance practice upon the Confederate steamer Richmond, and renewed it on Saturday. No damage resulted, however, and the enemy expended considerable ammunition to no purpose. In establishing a blockade of the Potomac the South materially interrupted the plans of the Lincolnians and we may reasonably expect some powerful demonstrations against the batteries which have so suddenly and effectually put a stop to navigation.