The Federal possession of these two forts rendered Columbus untenable for the Confederates, and on March 2 they evacuated it. This was followed by the fall of New Madrid on March 13, and of Island No. 10 on April 7. At the latter place between 6000 and 7000 Confederates surrendered. Thus was the Federal wedge being driven steadily deeper down the channel of the Mississippi. Soon after this good service of the gunboats on the Western rivers, the salt-water navy came in for its share of glory. On March 8 the ram Virginia, late Merrimac, which had been taking on her mysterious iron raiment at the Norfolk navy yard, issued from her concealment, an ugly and clumsy, but also a novel and terrible monster. Straight she steamed against the frigate Cumberland, and with one fell rush cut the poor wooden vessel in halves and sent her, with all on board, to the bottom of the sea. Turning then, she mercilessly battered the frigate Congress, drove her ashore, and burned her. All this while the shot which had rained upon her iron sides had rolled off harmless, and she returned to her anchorage, having her prow broken by impact with the Cumberland, but otherwise unhurt. Her armor had stood the test, and now the Federal government contemplated with grave anxiety the further possible achievements of this strange and potent destroyer. But the death of the Merrimac was to follow close upon her birth; she was the portent of a few weeks only. For, during a short time past, there had been also rapidly building in a Connecticut yard the Northern marvel, the famous Monitor. When the ingenious Swede, John Ericsson, proposed his scheme for an impregnable floating battery, his hearers were divided between distrust and hope; but fortunately the President's favorable opinion secured the trial of the experiment. The work was zealously pushed, and the artisans actually went to sea with the craft in order to finish her as she made her voyage southward. It was well that such haste was made, for she came into Hampton Roads actually by the light of the burning Congress. On the next day, being Sunday, March 9, the Southern monster again steamed forth, intending this time to make the Minnesota her prey; but a little boat, that looked like a "cheese-box" afloat, pushed forward to interfere with this plan. Then occurred a duel which, in the annals of naval science, ranks as the most important engagement which ever took place. It did not actually result in the destruction of the Merrimac then and there, for, though much battered, she was able to make her way back to the friendly shelter of the Norfolk yard. But she was more than neutralized; it was evident that the Monitor was the better craft of the two, and that in a combat _à outrance_ she would win. The significance of this day's work on the waters of Virginia cannot be exaggerated. By the armor-clad Merrimac and the Monitor there was accomplished in the course of an hour a revolution