meunier: formation of magmatic gases 215 



mechanism of the ''irregularities" of the earth's surface. Thus 

 arise the alternate syncHnal and anticHnal folds, with all their 

 variants; thus are formed the faults, which in all mountain chains, 

 wherever their cross section is exposed, are found in such vast 

 numbers as to constitute an essential element in orogeny; thus 

 are started the fissure eruptions the study of which has already 

 been so fruitful of results. 



Having recalled these two points, we have now to inquire 

 what will be the necessary consequences of their coexistence. 

 The zone of maximum contraction is evidently situated at a 

 depth which, though not yet accurately measured, is nevertheless 

 indicated by the location of earthquakes. From that zone as a 

 focus starts the impulse which gives rise to the subterranean 

 phenomena. Along the plane of contact, of any given extent, 

 between the internal incandescent zone and the superposed zone 

 impregnated with volatiUzable material, what will happen when a 

 part of the latter zone is covered by the rocks intruded from 

 below? It will form a wedge, as it were, clamped between two 

 very hot bodies : beneath it, the rocks remaining in their previous 

 relative positions, and above it, the rocks that have been intruded 

 along the plane of injection. Its temperature will necessarily 

 rise. To understand the resulting effects, we may well turn for 

 information to the celebrated experiments by Senarmont. 



Suppose that mineral matter is subjected to heat in an elastic 

 atmosphere consisting of those vapors very appropriately called 

 mineralizers, chiefl}" superheated water. A relatively moderate 

 temperature — of a few hundred degrees — will then suffice, without 

 any necessary change in composition, to produce the long series 

 of crystallized substances characteristic of volcanic rocks. On 

 this point the laboratory results, conclusive in themselves, may 

 be further supplemented with the informaton furnished by 

 certain natural localities, where human action has caused synthe- 

 ses of the same kind to assume geologic proportions. Fire started 

 as a result of mining operations in certain deposits of combustible 

 material, that is, in coal mines, causes the metamorphosis of clays 

 into crystalline agregates of minerals identical with those of the 

 lavas, such as ferro-magnesian silicates (pyroxene) and aluminium 



