186 Mr Solly on the Motion of Earthquakes. 



May we not then assume as correct, both explanations of 

 the mode in which earthquakes are supposed to transmit their 

 motions \ by the undulations of the subterranean fluids, and 

 by the vibrations of the superficial crust. Mr Milne has 

 pointed out that most of the English and Scotch earthquakes, 

 being confined to mere patches of the earth's surface, must be 

 due to the latter ; and, on the other hand. Professor Phillips 

 remarks that rocks being very imperfectly elastic, owing to 

 the numerous divisions which intersect them, cannot be sup- 

 posed capable of transmitting vibrations to any very consider- 

 able distance. To the subterraneous undulation we may at- 

 tribute the motion ; which passing under, without shaking the 

 Andes, was felt " evenly gentle" at Mendoza. To the super- 

 ficial vibration we may attribute the fall of the mountain 

 peaks at Tacna, the shivered rocks at Quiriquina, and those 

 strange rotatory motions referred to by Mr Darwin,* and of 

 which T have seen striking examples at Tacna and at Lima. 

 In the latter case the upper stone of a lofty obelisk was turn- 

 ed, in 1828, in a manner precisely similar to that in Calabria, 

 of which Mr Lyell has given a drawing, t 



The question occurred to me some time since, though I 

 should scarcely have ventured to mention it without having 

 seen Professor Keilhau's remarks in your last number, whether 

 frequent vibration, repeated during long series of ages (which, 

 according to Mr Darwin, + I will suppose to accompany the 

 elevation of a mountain chain), may not have produced consi- 

 derable changes, all tending to crystalline forms, in the mole- 

 cular constitution of some of the basaltic and metamorphic 

 rocks. It is now an ascertained fact, though but recently 

 acknowledged, that malleable iron, and other metals in a 

 fibrous state, assume the crystalline, under the operation of 

 vibration, and without the accession of heat.§ My friend Mr 

 William Lucas, (this year the President of our Sheffield So- 



* Journal of Researches, p. 376. 



t Principles of Geology, 6th edit, vol. ii. p. 336. 



X Journal of Researches, p. 380 ; and Geological Observations on Vol- 

 canic Islands, pp. 95 and 129. 



§ The axle-trees of railway carriages, and the holding down pins in 

 iron works, afford familiar instances. 



