The tinge of regret with which we leave Harper's Ferry is mitigated by the hope that greater wonders may lie beyond. In two miles the railroad, as if willing to carve out a picture-frame in which the heroic river may be viewed, excavates the "Potomac Tunnel," as it is named, through which the water is seen like a design in _repoussé_ silver, with two or three emerald islands in it for jewel-work. The perforation is eighty feet through, but in contrast with its rocky breadth our picture-frame is not too deep: whenever we shift our position, the view seems to increase in art-beauty, and as a final comprehensive picture it recedes and crowds under the spandrels of the arch the whole mountain-pass, with the confluence of the two rivers in the finest imaginable aspect. Poor Martinsburg! during the rebellion a mere sieve, through which the tide of war poured back and forth in the various fluctuations of our fortune! It is said to have been occupied by both armies, alternately, fifteen times. The passenger sees it as a mere foreground of big restaurant and platform, with a conglomeration of village houses in the rear--featureless as the sheep which the painter of Wakefield put in for nothing. One incident, however, supervenes. An old man, with positive voice and manners, and altogether a curious specimen in looks, gait and outfit, comes through the train with a pannier of apples and groundnuts. He is pointed out as one of the men of importance in Martinsburg, owning a row of flourishing houses. With the anxious servility which wealth always commands, we purchase an apple of this capitalist, blandly choosing a knotty and unsalable specimen. Pretty soon, as we look over into Maryland, we have indicated for us the site of old Fort Frederick, until lately traceable, but now completely obliterated. It was an interesting relic of the old Indian wars. Shortly after Braddock's defeat on the Monongahela, when the Indians had become very bold, and had almost depopulated this part of Maryland, Fort Frederick was erected by Governor Sharpe as a menace, and garrisoned with two hundred men. It was an immediate moral victory, awing and restraining the savages, though no decided conflict is known to have occurred from its construction to its quiet rotting away within the present generation. Those were the days when Frederick in Maryland and Chambersburg in Pennsylvania were frontier points, the Alleghanies were Pillars of Hercules, and all beyond was a blank! Still continuing our course on the Virginia side of the Potomac, through what is known in this State as the Virginia Valley, while in Pennsylvania the same intervale is called the Cumberland Valley, we admire the increasing sense of solitude, the bowery wildness of the river-banks, and the spirited freshness of the hastening water. At a station of delightful loneliness we alight.