Burning of a Bridge on the Northern Central Railroad, etc.
Raltimore, April 20P. M.
--The Melville Bridge between Woodbury and Mount Washington, on the Northern Central Railroad, has been burnt down.
It is reported that the Northern troops are at the Relay House, a station on the Northern Central Railroad.
The Melville Bridge is a short bridge--sixty feet span.
It is reported that the Railroad Ferry Boat at Havre-de-Grace, has been seized by the Marylanders, in order to prevent the passage of Northern troops.
The only two possible land routes by which the Northerners, who are reported to be on the North side of the Susquehanna to the number of from three to seven thousand, can now possibly reach Baltimore, and consequently Washington, are by returning to Philadelphia and taking the Pennsylvania Central Road, or to march up to Port Deposit, a distance of twelve miles from Havre-de-Grace, where there is, as yet, an unobstructed passage, and from there to reach the Baltimore and Wilmington Road.
The troops, however, by themselves, or reinforced by the New York Seventh Regiment, may be advancing on Washington by water. 