EARTHQUAKES AND VOLCANOES. 



25. Earthquakes are often attended, though not at all, as is 

 commonly supposed, preceded by awful subterranean sounds. 

 These noises, however, appear to have no relation whatever to the 

 violence of the shock. Some of the most tremendous of these 

 convulsions have, on the contrary, been unaccompanied by any 

 noise whatever. This was the case with the great earthquake of 

 Biobamba already mentioned, one of the most terrible catastrophes 

 of its class which has been recorded in the physical history of 

 the globe. 



The noises which are heard most commonly occur after the 

 shock, and seldom at the place where the earthquake has the 

 greatest violence. In the case of the earthquake of which 

 Tacunga and Hambato were the centre and points of greatest 

 action, no noise was heard at these places, but violent sub- 

 terraneous detonations were heard at Quito, which is fifty-five 

 miles, and at Ibarra, about one hundred miles distant from those 

 points, at twenty minutes after the shock. 



The subterranean thunder, if it may be so called, is sometimes 

 heard at places situate beyond the limits of the shocks. Thus in 

 the case of the violent earthquake which occurred at Lima and 

 Callao, on 28th October, 1746, a noise resembling a clap of 

 subterranean thunder was heard at Truxillo, where no shock 

 whatever was felt, nor even the least trembling of the ground. 



Sometimes the subterranean thunder is heard after the shocks 

 have ceased. The great earthquake which occurred on 16th 

 November, 1827, in New Grenada, and was described by 

 Boussingault is an example of this. Some time after the cessation 

 of the shocks, subterranean detonations were heard at regular 

 intervals of half a minute along the whole Cauca valley. 



26. The character of the noise attending earthquakes has 

 differed greatly in different cases. Sometimes it has been a 

 rolling sound like that of thunder, or the discharges of cannon in 

 rapid succession. Sometimes it is described as resembling the 

 clanking of chains. At Quito it is often sudden, like a near 

 thunder-clap, and sometimes it is clear and ringing like the 

 clashing of glass, as if enormous masses of vitrified matter were 

 shattered in subterranean caverns. 



27. Owing to the fact that solid bodies are good conductors of 

 sound, the sonorous undulations being propagated through them 

 with a velocity ten or twelve times greater than through the 

 atmosphere, the subterranean noise developed in these convulsions 

 may be heard at great distances from the seat of the agency 

 which produces it. During a violent eruption of the volcano of 

 St. Vincent, one of the smaller "West India Islands, and while a 

 prodigious torrent of lava issued from it, a loud noise resembling 



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