There is scarcely a spot known on the surface of the earth, which does not show strong evidence of having, at some former period, been the bed or bottom of some sea or lake. Some of these evidences may be seen in the strata or layers of earth forming the sides of the cliffs which abut on the sea-shore, and which could not have been produced by any other agency; these strata contain so many marine shells and other matters peculiar to the sea, that the fact does not admit of doubt that they were there produced. These same strata are met with throughout the land; in sinking wells and mines, the same strata are cut through, and have a known and uniform succession, with but few exceptions; the cliffs, however, are the most convenient places to see these strata. That the same process of alteration in the position of the water and land is still going forward, is shown by many evidences, such as towns which were once on the sea-shore, being now some distance from it, as the City of Norwich, and in other cases the reverse. The chalk cliffs at Dover, Ramsgate, &c., show the action of the sea in the corroded state they present, and slips or falls of great masses which have been undermined by the sea, are frequently occurring. [Illustration: CLIFFS, SHOWING STRATA.] The ancient town of Ravenspurn, at which Henry IV. landed, has entirely disappeared, and others, recorded to have been situated on the shore, have now only their names left. The parts of the shore most rapidly corroded by the sea, are those composed of sand, chalk, and clay, while those composed of the harder kinds of sandstone or of granite, have been but little wasted away, so that they project and form the headlands, while in many cases deposits of mud have extended them. There are many other causes which determine the elevation or depression of the land, besides the action of the sea and earthquakes, such as winds, frosts, &c. [Illustration: CHALK CLIFFS, DOVER.] [Illustration: GREAT WAVES AT SEA.] [Illustration: DEAD CALM.]