Feb. 1, 1886.] 



KNOAA^LEDGE 



119 



circular or rotary concussions. Walls bej'ond tlie town 

 were twisted round without being flung down; rows of 

 trees whicli had been parallel were deflected in the mo.st 

 remarkable manner ; and the direction of the ridges of 

 fields covered with various kinds of grain was observed 

 to be altered by the effects of the earthquake. 



Humboldt, it may be mentioned, explains in a some- 

 what unnatural manner the jjeculiar effects we have 

 spoken of above. He conceives that the fact of the 

 furniture of one house being found under the ruins of 

 another, seems to show that the movement was first 

 directed downwards, then horizontally, and then upwards. 

 This appears to me wholly improbable. In the first place 

 it has been almost constantly observed that the upward 

 motion (in earthquakes which exhibit perpendicular 

 vibiMtions) precedes the downward ; and secondly, hf.d 

 tlie downward motion taken place first, it seems most 

 probable that neighbouring houses would have sunk side 

 ly side, so that the following horizontal movement would 

 only have resulted in the forms of destruction ordinarily 

 observed in earthquakes. The more natural view seems 

 to be that there was first a violent upward movement, 

 flinging the less firmlj- built hou.ses bodily upwards, and 

 merely destroying others ; then immediately followed a 

 downward movement and a horizontal one, bringing the 

 latter class of houses beneath the falling ruins of the 

 others. Or it may be that so violent was the first upward 

 movement, that the upper parts of fA\ buildings were 

 flung into the air, whence — not partaking in the horizontal 

 movement which displaced the foundations and lower 

 part of the houses — they fell in ruins over the debris of 

 buildings they had not belonged to originally. An 

 ni)ward, followed b}- a downward, and then by a hori- 

 zontal movement, might result in either form of demo- 

 lition, or in both. 



A short time after the destruction of Riobamba, a 

 fearful subterranean rumbling, resembling the loudest 

 thunder-peals, was heard under the cities of Quito and 

 Ibarra, the former more than a hundred miles from 

 Riobamba. 



EARTHQUAKE NOISES. 



The subterranean noises heard during eai-thquakes 

 are sometimes singularly striking. The nature of the 

 noises is very various, says Humboldt, "rolling, rattling, 

 clftuking like chains, occasionally like thunder close 

 at hand ; or it is clear and ringing, as if masses of 

 obsidian or other vitrified matters were struck in 

 caverns underground." These noises are not only 

 heard much farther off than they could be if they were 

 transmitted in the air, but they travel much more 

 rapidly. In 1744, when the great eruption of Cotopaxi 

 took place, subterranean noises were heard at Honda, 

 on the Rio Maddalena. The crater of Cotopaxi, 17,000 

 feet above the level of Quito, is separated from it " by 

 the colossal mountain-masses of Quito, Pasto, and 

 Papayan, by innumerable valleys and precipices, and 

 by an actual distance of no less than .500 geographical 

 miles." The eruption which took place in the island of 

 St. Vincent on April 30, 1812, produced subterranean 

 noises resembling the loudest peals of thunder in Carac- 

 cas, in the plains of Calabozo, and on the blanks of the 

 Rio Apure, a distance of upwards of 700 geographical 

 miles. " This, in respect of distr.nce," says Humboldt, 

 "was as if an eruption of Mount Yesuviu.s were to be 

 heard in the north of France." 



But it is remarkable that subterranean rumblings and 

 bello wings are sometimes heard when neither an earth- 

 quake nor the kindred phenomenon — a volcano — is in 

 progress. "Sonorous phenomena," Humboldt tells us, 



" when accompanied by no perceptible shocks, leave a 

 remarkably deep- impression even with those who have 

 long dwelt in districts subject to repeated earthquakes." 

 A singular instance occurred in the year 1784, in the 

 high lands of Mexico. A sound was heard as of heavily 

 rumbling thunder alternating with sharp explosive 

 biirsts beneath the feet of the startled inhabitants of 

 Guanaxato. The subterranean bellowings and thunder- 

 ings {branridos y truenos subterraneos') grew gradually 

 more and more intense, and then decreased as gradually. 

 Terrified by a phenomenon which seemed to forewarn 

 them of an approaching and terrible catastrophe, the in- 

 habitants fled from the town, leaving great piles of silver 

 bars a prej- to bands of robbers. But after r. time the 

 more courageous returned and repossessed themselves 

 of their treasure. For one month the subterranean 

 grumblings were heard at intervals, though neither on 

 the sui-face of the earth, nor in the silver mines 500 j^ards 

 beneath it, was any movement of the earth perceptible. 



THE EARTHQUAKE AS A RESTOKlNCx POWER. 

 We are so in the habit of regarding the earthquake as 

 an agent of destruction, that it may sound paradoxical to 

 assert that the phenomenon is surpassed by no other as a 

 regenerative and restorative agent. Yet this is strictly 

 the case. But for earthquakes our continents would 

 continuallj' — however slowly — diminish in extent 

 through the action of the sea- waves upon their borders, 

 and of rain and rivers on their interior surfaces. " Had 

 the primeval world been constructed as it now exists," 

 says Sir John Hei-sehel, " time enough has elapsed, and 

 force enough, ^directed to that end, has been in activity, 

 to have long ago destroyed evevy vestige of land." 

 It is to the reproductive energy of the earth's internal 

 forces that we are alone indebted for the very existence 

 of dry land. To the same cause, undoubtedly-, we owe 

 that gradual jirocess of change in the configuration of 

 continents and oceans which has been for ages and 

 still is in progress — a process the benefit derived fmm 

 which cauuot possibly be called in question. Our 

 forests and our fields derive their nourishment from 

 soils propart'd, for long ages, beneath the waves of 

 ocean ; our stores of coal and cif many other important 

 minerals have been in like manner jirepared for our 

 use during the long intervals of their submergence ; we 

 build our liouses, even, with materials many of which 

 owe their perfect adaptation to our wants to the 

 manner in which they have been .slowly deposited on 

 what was once the bed of ocean, and compressed to a 

 due solidity and firmness of texture beneath its depths. 

 ]f it is indeed true, as Humboldt asserts, that "the 

 destiny of mau is in part dependent on the fa.shion 

 of the outer crust of the globe, on the partitioning of 

 continents, on the direction of the mount:iiu chains 

 which traverse them, and on the distribution of land 

 .and water," then we mu.st look upon the earthquake as 

 the most important of all those agencies which tend to 

 the renovation of our terrestrial globe. So far from 

 dreading lest the earth's subterranean forces should 

 acquire new energies, we ought rather to fear lest they 

 should lose their force. We may, therefore, gladly 

 hail the opinion of the gi'eat geologist who asserts that 

 "the energy of subterranean movtments has always 

 been uniform as reg.ai'ds the whole earth. The force 

 of earthquakes," adds Lyell, " may for a cj'cle of years 

 have been invariably confined, as it is now, to large but 

 determinate spaces; ' gri,dually, however, this fi rce 

 .shifts in position, so that other regions, for agts at rest, 

 become " in their turn the grand theatre of action." 



