extent just equal to half the area of France, or about five-sixths of the area of Great Britain and Ireland. If we suppose the elevation to have been only three feet on an average, it will be seen that the mass of rock added to the continent of America by the movement, or, in other words, the mass previously below the level of the sea, and after the shocks permanently above it, must have contained fifty-seven cubic miles in bulk; which would be sufficient to form a conical mountain two miles high (or about as high as Etna), with a circumference at the base of nearly thirtythree miles. We may take the mean specific gravity of the rock at 2.655,-a fair average, and a convenient one in such computations, because at such a rate a cubic yard weighs two tons. Then, assuming the great Pyramid of Egypt, if solid, to weigh, in accordance with anestimate before given, six million tons, we may state the rock added to the continent by the Chilian earthquake to have more than equalled 100,000 pyramids. But it must always be borne in mind that the weight of rock here alluded to constituted but an insignificant part of the whole amount which the volcanic forces had to overcome. The whole thickness of rock between the surface of Chili and the subterranean foci of volcanic action, may be many miles or leagues deep. Say that the thickness was only two miles, even then the mass which changed place and rose three feet, being 200,000 cubic miles in volume, must have exceeded in weight 363 million pyramids. It may be useful to consider these results in connexion with others already obtained from a different source, and to compare the working of two antagonist forces-the levelling power of running water, and the expansive energy of subterranean heat. How long, it may be asked, would the Ganges require, according to data before explained, to transport to the sea a quantity of solid matter equal to that added to the land by the Chilian earthquake? The discharge of mud in one year by the Ganges equalled the weight of sixty pyramids. In that case it would require seventeen centuries and a half before the river could bear down from the continent into the sea a mass equal to that gained by the Chilian earthquake. In about half that number of centuries, perhaps, the united waters of the Ganges and Burrampooter might accomplish the opera tion. Aleppo, 1822.-Ionian Isles, 1820.-When Aleppo was destroyed by an earthquake in 1822, two rocks are reported to have risen from the sea near the island of Cyprus ;* and a new rocky island was observed in 1820 not far from the coast of Santa Maura, one of the Ionian Islands, after violent earthquakes.† Cutch, 1819.-A violent earthquake occurred at Cutch, in the delta of the Indus, June 16, 1819. (See annexed Map, Plate V.) The principal Journ. of Sci., vol. xiv. p. 450. + Von Hoff, vol. ii. p. 180. |