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Show CONCEPCION· March, 1835. tain. The side walls, though exceedingly fra~tured, yet re-mar. ne d s tan din g; but the vast buttresses (at nght angles t.o them and therefore parallel to the walls that fell) were m man; cases cut clean off, as if by a chisel, and hurled to the ground. Some square ornaments on the. coping_ of these ~~me wa ll s were move d by the earthquake mto a diagonal positi.o n. The buttresses of the church of La Merced, at Valparaiso, and some heavy pieces of furniture in the rooms, were similarly affected by the shock o_f 1~22.* ~r. Lye~l t has also given a drawing of an obehsk m Calabna, of whiCh the separate stones were partially turned round. I~ these instances, the displacement at first appears to be owmg to a vorticose movement beneath each point thus affected ; but such can hardly be the case. May it not be caused by a tendency in each stone to arrange itself in . som~ parti?ular position, with respect to the lines of vibratiOn, - m a manner somewhat similar to pins on a sheet of paper, or on a board when it is shaken? Generally speaking, arched doorways o~ windows stood much better than any other kind of building. Nevertheless, a poor lame old man, ~ho had been in the habit, during trifling shocks, of crawlmg to a certain doorway, was this time crushed to pieces. I have not attempted to give any detailed description of the appearance of Concepcion, for I feel it is quite impossible to convey the mingled feelings with which one beholds such a spectacle. Several of the officers visited it before me, but their strongest language failed to communicate a just idea of the desolation. It is a bitter and humiliating thing to see works, which have cost men so much time and labour, overthrown in one minute ; yet compassion for the inhabitants is almost instantly forgotten, from the interest excited in finding that state of things produced in a moment of time, which one is accustomed to attribute to a succession of ages. In my * Miers's Chile, vol. i., p. 392. t Lyell's Principles of Geology, chap. xv., book ii. March, 1835. EARTHQUAKE WAVES. 377 opinion, we have scarcely beheld since leaving England, any other sight so deeply interesting. In almost every severe earthquake which has been described, the neighbouring waters of the sea are said to have been greatly agitated. The disturbance seems generally, as in the case of Concepcion, to have been of two kinds : first, at the instant of the shock, the water swells high up on the beach, with a gentle motion, and then as quietly retreats; secondly, some little time afterwards, the whole body of the sea retires from the coast, and then returns in great waves of overwhelming force. The first and less regular movement seems to be an immediate consequence of the earthquake differently affecting a fluid and a solid, so that their respective levels are slightly deranged. But the second case is a far more important phenomenon, and at first appears of less easy explanation. In reading accounts of earthquakes, and especially of those on the west coast of America, as collated from various authors by Sir W. Parish,* it is certain that the first great movement of the waters has been that of retiring. Several hypothesest have been invented to explain this fact. Some have supposed it owing to a vertical oscillation in the land, the water retaining its level: but this can hardly happen, even on a moderately shoal coast; for the water near the land must partake of the motion of the bottom. Moreover, as Mr. Lyell has urged, a change of level in the land will not account for movements in the sea, of a similar nature, affecting islands distant from the line of uplifted coast. This occurred at Madeira during the famous Lisbon earthquake. Juan Fernandez also offers a parallel instance ; for the sea was disturbed there much in the same manner as on the coast of Chile. The whole phenomenon, it appears to me, is due to a common undulation in the water, proceeding from a line or point of • Sir W. Parish had the kindness to lend me the original manuscript, which was read before the Geological Society, March 5th, 1835. t Lyell's Geology, book ii., ch. xvi. |