122 m. de beaumont's geology of mountains. 



at least those which are at the same time the most striking and re- 

 cent, are composed of a certain number of small chains, ranged 

 parallel to the semi-circumference of the earth's surface, and occu- 

 pying a zone of much greater length than breadth, and of which the 

 length embraces a considerable fraction of one of the great circles 

 of the terrestrial sphere. It may be observed respecting the hypo- 

 thesis of each of these mountain-systems being the product of a 

 single epoch of dislocation, that it is easier geometrically to con- 

 ceive the manner in which the solid crust of the globe may be ele- 

 vated into ridges along a considerable portion of one of its great 

 circles, than that a similar effect may have been produced in a more 

 restricted space. 



However well established it may be by facts, the assemblage of 

 which constitutes positive geology, that the surface of the globe has 

 presented a long series of tranquil periods, each separated from 

 that which followed it by a sudden and violent convulsion, in which 

 a portion of the earth's crust was dislocated, — that, in a word, this 

 surface was ridged at intervals in different directions ; the mind 

 would not rest satisfied if it did not perceive among those causes 

 now in action, an element fitted from time to time to produce dis- 

 turbances from the ordinary march of the phenomena which we now 

 witness. 



The idea of volcanic action naturally presents itself when we 

 search, in the existing state of things, for a term of comparison with 

 these great phenomena. They nevertheless do not appear suscep- 

 tible of being referred to volcanic action, unless we describe it, with 

 M. Humboldt, to be the influence exercised by the interior of a 

 planet on its exterior covering during its different stages of refri- 

 geration. 



Volcanos are frequently arranged in lines following fractures 

 parallel to mountain chains, and which originate in the elevation 

 of such chains j but it does not appear to me that we can thence 

 regard the elevation of the chains themselves as owing to the action 

 of volcanic foci, taking the words in their ordinary and restricted 

 sense. We can easily conceive how a volcanic focus may produce 

 accidents circularly and in the form of rays from a central point, 

 but we cannot conceive how even many united foci could produce 

 those ridges which follow a common direction through several de- 

 grees. 



Volcanic action, such as it is commonly understood, could not, 

 therefore, be itself the first cause of these great phenomena, but vol- 



