meunier: theory of volcanoes 641 



crust, which at any given moment is too wide for its contentSj 

 and that this is the sole cause of the characteristic superposi- 

 tions observed in mountains. 



This, however, does not yet suffice to explain completely the 

 origin of mountains, and it is proper to note that the process just 

 described is strictly confined to the underground regions. In 

 order that a mountain may be formed another thing is neces- 

 sary: the block that has been compressed in the underground 

 region has to be raised by tangential reactions, causing a pro- 

 tuberance that rises above the general surface of the planet. 

 The gigantic tuberosity of Thibet, in the heart of the Asiatic 

 continent, is a type. 



Space will not admit of presenting the arguments which prove 

 that the compression and transfer on the incline planes of geo- 

 clases can take place only in a certain portion of the crust. The 

 deeper portions are still too hot to admit of the production and 

 maintenance of gliding planes in their plastic substance, while 

 in the outer parts the porosity and compressibility of the rocks 

 constituting the substratum, opposing their inertia to the propa- 

 gation of vibrations, protect the superficial strata against exces- 

 sive mechanical shocks, which would constitute an insuperable 

 obstacle to the development of external phenomena, such as the 

 manifestations of organic life. 



Without dwelling on this subject let us note merely that the 

 mechanical deformations of the crust are not the only inevitable 

 consequences of the spontaneous cooling of the globe. 



Another fact of equal importance, and without which vol- 

 canism would be impossible, develops parallel with the first. 

 We have already noted that the lowering of the surface temper- 

 ature has led to the condensation of water, the fall of rain, and 

 the development of rivers, whose waters accumulate in the ocean 

 basins. Part of the water penetrates into the crust not only 

 by constant infiltration but by the burial of wet sediments under 

 later sediments, whereby water and other volatilizable matter 

 are imprisoned in the solid mass at constantly increasing depths 

 and are incorporated in a large part of the thickness of the crust. 



This being premised, we must next observe that the over- 



