

SUBTERRANEAN THUNDER. 



thunder unaccompanied by any trembling of the ground, was 

 heard at the distance of 632 miles to the south-west of the crater 

 on the plains of Calaboso, and on the banks of the river Apure, 

 one of the tributaries of the Orinoco. This noise was audible 

 over an area of nearly 50000 square miles. So far as distance 

 is concerned, this was as if a noise attending an irruption of 

 Vesuvius were heard at London. 



28. During the great eruption of Cotopaxi, one of the most 

 lofty peaks of the Andes, subterranean sounds like discharges of 

 artillery were heard at Honda, on the Magdalena river. This is 

 the more remarkable, inasmuch as the crater of Cotopaxi is not 

 only 18000 feet above the level of Honda, and the distance 

 measured in a direct line between the two points is 463 miles, but 

 vast mountain masses such as Quito, Pasto, and Popayan, as well as 

 innumerable valleys and ravines are interposed between them. 

 The sound was therefore evidently in this case propagated through 

 the solid crust of the earth from a great depth, and not through 

 the air. 



Another striking example of the propagation of sound from the 

 depths of the earth to great distances through its crust was pre- 

 sented in the case of the violent earthquake which occurred in 

 New Grenada, in 1835. On that occasion, subterranean thunder 

 was heard at Popayan, Bogota, Santa Martha, and Caraccas, and 

 also in Hayti, in Jamaica, and on the shores of Lake Nicaragua. 

 At Caraccas the thunder continued without any sensible trembling 

 of the ground for seven hours. 



It would appear that in some cases the solid telluric shell is 

 strong enough to resist the undulations of the subterranean 

 igneous fluid while it transmits the sonorous vibrations. It 

 is difficult to convey an adequate idea of the impression which 

 these terrible sounds, issuing from the depths of the earth, 

 produce, when they are not attended by any dynamical or 

 other phenomena. It is as if a preternatural voice coming 

 from below addressed the entire population. The listener waits 

 after each roll of the sound in an agony of suspense for what 

 may follow. 



29. One of the most remarkable examples of these subter- 

 raneous sounds unaccompanied by any disturbance of the surface 

 of the ground, was that which occurred in the great mining 

 regions of Mexico, in 1784, and which is known in that 

 country as the Bramidos subterraneos (subterraneous roaring) of 

 Guanaxuato. * 



* Humboldt, Essai Polit. sur la Nouv. Esp., vol. i., p. 303. Cosmos, 

 Trans, vol. i., p. 196, and note 187. 



157 



