640 meunier: theory of volcanoes 



basins, to which, by a ceaseless circulation, it always returns 

 after falling as rain and flowing over the land as storm water 

 and running water — aside from the large amount that seeps 

 into the ground, of which we will speak later on. 



Without entering into details which every one knows, I will 

 merely add, for the sake of clearness, that the deformations of 

 the earth's crust, constantly diminishing the diameter of the 

 planet, consist essentially in the transformation of a centripetal 

 action into a tangential compression, as is shown by the great 

 mountain ranges, whose natural escarpments so often and so 

 clearly reveal to us the internal structure. In these mountain 

 ranges beds of a great variety of rocks are seen resting one on 

 the other, which may be correlated with the strata of the plains, 

 but which have been modified in their mineral composition by 

 metam'orphism and in their relative position by orogenic forces. 



As regards the last-mentioned point, the essential fact is that 

 geologically old strata commonly rest on geologically younger 

 strata, which is exactly the reverse of what prevails in undis- 

 turbed sedimentary regions. When, for example, we climb the 

 Alps we first pass over very recent beds, such as the Tertiary 

 conglomerates of the Righi, next over Mesozoic deposits, " such 

 as the Cretaceous and Jurassic marbles of Mount Pilatus, next 

 over Paleozoic sediments, such as the Carboniferous shales of 

 the Mcede, etc., and only when we arrive at the top do we find 

 the primitive rocks, such as the gneisses of the Jungfrau. 



There can be no doubt that these strata were pushed along 

 nearly horizontal planes of fracture, with the result that they 

 now occupy a much smaller area than they did originally, while 

 their thickness has increased by superposition, as has just been 

 pointed out. Thus there has been a transfer of deep-seated 

 material over younger strata. It is necessary to recall this 

 commonplace notion, because it suffices to give us the viewpoint 

 needed for the present subject as regards everything relating to 

 the structure of mountain ranges, which for that matter varies 

 widely. 



Summarizing this first point, we see that the spontaneous 

 cooling of the globe gives rise to a tangential compression of the 



