178 COSMOS. 



markable that so many warm mineral springs retain their 

 composition and temperature unchanged for centuries, and 

 therefore must flow from fissures which appear to have un- 

 dergone no alteration either vertically or laterally. The 

 establishment of communications with higher strata would 

 have produced a diminution, and that with lower ones an 

 increase of heat. 



When the great eruption of the volcano of Conseguina (in 

 Nicaragua) took place on the 23rd of January, 1835, the 

 subterranean noise 25 (los ruidos subterraneos) was heard at 

 the same time on the island of Jamaica and on the plateau 

 of Bogot, 8740 feet above the sea, at a greater distance than 

 from Algiers to London. T have also elsewhere observed, 

 that in the eruptions of the volcano on the island of Saint 

 Vincent, on the 30th of April, 1812, at 2 o'clock in the 

 morning, a noise like the report of cannons was heard with- 

 out any sensible concussion of the earth over a space of 

 160,000 geographical square miles. 8 * It is very remarkable 

 that when earthquakes are combined with noises, which is 

 by no means constantly the case, the strength of the latter 

 does not at all increase in proportion to that of the former. 

 The most singular and mysterious phenomenon of subter- 

 ranean sound is undoubtedly that of the bramidos de Gua- 

 naxuato which lasted from the 9th of January to the middle 

 of February. 1784. regarding which I was the first to collect 

 trustworthy details from the lips of living witnesses, and 

 from official records (Cosmos, vol. i, p. 205). 



The rapidity of the propagation of the earthquake upon 

 the surface of the earth must from its nature be modified in 

 many ways by the variable densities of the solid rocky strata 

 (granite and gneiss, basalt and trachytic porphyry, Jurassic 

 limestone and gypsum), as well as by that of the alluvial 

 soil, through which the wave of commotion passes. It 



85 Acosta, Viajes cientificos d los Andes ecuatoriales, 1849, p. 56. 



26 Cosmos, vol. i, pp. 204 206 ; Humboldt, Relation ffistorique, 

 t. iv, chap. 14, pp. 31 38. Some sagacious theoretical observations by 

 Mallet upon sonorous waves in the earth and sonorous waves in the air 

 occur in the Brit. Assoc. Report, 1850, pp. 41 46, and in the Admiralty 

 Manual, 1849, pp. 201 and 217. The animals which in tropical coun- 

 tries are disquieted by the slightest commotions of the earth sooner 

 than man are, according to my experience, fowls, pigs, dogs, asses, and 

 crocodiles (CajtnnuH); the latter suddenly quit the bottom D the riveru, 



