Naval Engagement at Newport News.

Our dispatches this morning (detained yesterday by a break in the telegraph wires) detail a hardly contested naval engagement off Newport News. The iron clad rebel steamer Merrimac assisted by two other iron gun boats, the Jamestown and Yorktown, made a fierce attack upon the U.S. sailing frigates Cumberland and Congress, which had been towed up to the mouth of James river to keep the blockade and there left to their fate. Of course they were unable to do anything against the rebel iron steamers and the first was sunk and the latter captured. Subsequently the steam frigate Minnesota and the iron clad Monitor advanced against the rebel boats from Fortress Monroe, and a most severe engagement ensued, resulting in the crippling and disabling of the Merrimac, and the driving of the other boats back to Norfolk. The demonstration on Newport News was unsuccessful. A month ago, an officer on board the Congress wrote us how absurd it was to guard the James river with unwieldy sailing frigates without the assistance of steam gunboats. He prophesized then exactly what has just taken place.