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Show 374 CO:KCEl'ClON. March, 1835. under his protection, lived for the first week in a garden beneath some apple-trees. At first they were as merry as if it had been a picnic; but soon afterwards heavy rain caused much discomfort, for they were absolutely without shelter. In Captain FitzRoy's paper it is said that two explosions, one like a column of smoke, and another like the blowing of a great whale, were seen in the bay of Concepcion. The water also appeared every where to be boiling; and it " became black, and exhaled a most disagreeable sulphureous smell." I am informed by Mr. Alison, that during the earthquake of 1822 these last-mentioned circumstances occurred in the bay of Valparaiso. The two great explosions in the first case must no doubt be connected with deep-seated changes; but the bubbling water, its black colour and fetid smell, the usual concomitants of a severe earthquake, may, I think, be attributed to the disturbance of mud containing organic matter in decay. In the bay of Callao, during a calm day, I noticed, that as the ship dragged her cable over the bottom, its course was marked by a line of bubbles. The lower orders in Talcuhano thought that the earthquake was caused by some old Indian women, who two years ago having been offended, stopped the volcano of Antuco. This silly belief is curious, because it shows that experience has taught them to observe the constant relation between the suppressed activity of volcanoes, and the trembling of the ground. It was necessary to apply the witchcraft to the point where their knowledge stopped; and this was the closing of the volcanic vent. This saying is the more odd in this particular instance, because the result of Captain FitzRoy's investigation was to discountenance the belief that Antuco (whatever might have been the case with the volcanoes further northward) was any way affected. The town of Concepcion was built in the usual Spanish fashion, with all the streets running at right angles to each other. One set ranged S.W. by W. and N.E. by E., and the other N.W. by N. and S.E. by S. The walls in the former direction certainly stood better than those in the March, 1835. DIHECTIO~ OF VIBRATIOX. 375- other. Captain FitzRoy* has likewise remarked, that the greater number of the masses of brickwork were thrown down towards the N .E. Both these circumstances per- · fectly agree with the general idea of the undulation havino-o come from the S.W.; in which quarter subterranean noises were also sometimes heard. It is evident on this supposition, that the N.W. and S. E. walls, being nearly coincident with the line of undulation (or with the crests of the successive waves), would be much more likely to fall than those which had their extremities presented towards the point whence the vibration proceeded; for, in the first case, the whole wall would be thrown at the same moment out of its perpendicular. This may be illustrated by placing books edgewise on a carpet, and then, after the manner suggested by Michell, imitating the undulations of an earthquake : it will be found, that they fall with more or less readiness, according to their direction. The fissures in the ground, though not uniform, generally had a S. E. and N.W. direction ;t and therefore they corresponded to the lines of principal flexure. Bearing in mind all these circumstances, which so clearly point to the S. W. as the chief focus of disturbance, it is a very interesting fact that the island of S. Maria, t situated in that quarter, was during the general uplifting of the land (to which l shall presently refer) raised to nearly three times the altitude of any other part of the coast. The different resistance offered by the walls, according to their direction, was well exemplified in the case of the cathedral. The side which fronted the N.E. presented a grand pile of ruins, in the midst of which door-cases and masses of timber stood up, as if floating in a stream. Some of the angular blocks of brickwork were of great dimensions ; and they had been rolled to a distance on the level plaza, like fragments of rock round the base of some high moun- * Sketch of Surveying Voyages of Adventure aud Beagle by Captain FitzRoy, Royal Gcograph. Journal, vol. vi., p. 320. t Ditto, p. 327, et pas~im. |
