348 



Mount Ararat, affected equally the summits of mountains and 

 the bottoms of valleys. I myself have witnessed extreme 

 dislocations during earthquakes in the more northern Peru- 

 vian portions of the same chain of South American mountains, 

 the Cordillera of the Andes, to which I have already re- 

 ferred as unaffected in 1822 and 1835 by the most violent 

 littoral shocks, dislocations by which the loftiest peaks have 

 been overthrown, and the whole outline of the mountains 

 altered. 



It seems to me, therefore, impossible to maintain that the 

 propagation of the motion is regulated by or dependent on 

 "the mechanical structure of the mineral species," although 

 it may sometimes be modified thereby. 



The conviction which has forced itself on my mind by the 

 examination of all the evidence which I have been able to 

 collect on this subject is, that the motion of earthquakes is 

 transmitted in two ways, generally more or less simultaneous, 

 but different in their effects, namely, by the undulations of 

 subterraneous liquids or fluids, and by the vibration of the 

 earth's superficial crust. 



Mr. David Milne has excellently 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 supposed capable 

 of transmitting vibration to any very considerable distance. 

 To the subterranean undulations we might, then, attribute the 

 extent of very extensive earthquakes, such as that of Lisbon 

 on the 1st November, 1755, which has been calculated to have 

 shaken near one-twelfth of the whole surface of the globe ; 

 also the motion which, passing under without shaking the 

 Andes, has extended from the shores of the Pacific to 

 Mendoza and St. Juan. If the interior of the globe be an 

 intensely heated liquid or fluid substance, we can readily 



