THE CAUSE OF EARTHQUAKES. 283 



analysis of the solid materials which are daily carried 

 away by many of our springs. In limestone districts 

 this is very great. Prof. Ramsay estimates that the 

 mineral matter discharged annually by the hot springs 

 of Bath is equivalent in bulk to a column 140 feet 

 in height and 9 feet in diameter. At San Filippo, in 

 Tuscany, the solid matter discharged from the springs 

 has formed a hill a mile and a quarter long, a third of 

 a mile broad, and 250 feet in thickness.^ Many other 

 examples of subterranean chemical degradation will be 

 found in text-books of geology. 



By this chemical action large cavernous hollows are 

 produced. Beneath a volcano it is probable that liquid 

 material immediately takes the place of that which is 

 ejected, and that hollows are not formed as in the case of 

 chemical degradation. If a cavern becomes too large, it 

 eventually collapses. 



Of the falling in of large excavations we have 

 examples in large mines. As a consequence, not only is 

 a trembling produced, but also a noise, which is so like 

 that produced by certain earthquakes that the South 

 American miners have but one word, ' bramido,' to ex- 

 press both.2 



Boussingault, who was an advocate for the theory that 

 many earthquakes are produced by the sinking of the 

 ground, calls attention to the fact that we have evidences 

 of the subsidence of great mountains, like the Andes, the 

 districts around which are so well known for their earth- 

 quakes. Capac Urcu is one of these mountains which 

 legends tell us has decreased in height. 



The variation in the height of mountains is a subject 

 which deserves attention. That mountains may possibly 

 be hollow, we have the remarkable results attained by 

 ' Lyell, Princij}les, vol. i. p. 402. « Fuchs, p. 464. 



