There are so many lakes of salt, which are completely isolated and so many miles from the sea, that it is next to impossible to account for their existence if we do not ascribe them to volcanic action. If they are situated in low-lying districts, we may justly presume that at one time the sea must have been present, or that the deposition must have resulted from occasional, or tidal, overflow of salt water; but when they are many miles from the coast, and many feet above or below the sea-level, then they may be due to volcanic agency; and we shall find further on several other salt lakes of variable depths or altitudes which would seem to corroborate this hypothesis. The sea is undoubtedly a most formidable agent in the disintegration of land, and often destroys whole tracts, forcing its resistless waves into the interior of continents, and then, owing to some unexplained cause, retiring to its original boundary. This may take centuries to complete, for revolutions effected by nature are not accomplished speedily, unless there is some sudden spasmodic upheaving, arising from earthquakes or storms. In 1282, the isthmus uniting Friesland with the north of Holland was totally destroyed by violent storms. In our own country a similar phenomenon occurred in the year 1475, when a large tongue of land at the mouth of the Humber was entirely broken up and carried away by the sea. In 1510 an irruption of the Baltic formed the Frische-Haff, an opening 6000 feet broad, and from twelve to fifteen fathoms in depth. The eastern coast of England is continually receding, owing to the encroachment of the sea. The rate of encroachment of the sea at Owthorne, in Yorkshire, is reckoned at four yards in every year, and several villages have been swallowed up by the ocean; and in like manner the cliffs of Norfolk and Suffolk are suffering a continual decay.