214 meunier: formation of magmatic gases 



One of the principal effects of the recently formed crust has 

 been to imprison the entire nuclear region of the earth, and thus 

 to isolate it. The progressive thickening of the crust has pro- 

 duced a growing difference of temperature between its external 

 or epidermic region and its internal parts, which have only recently 

 passed into the solid state. Aqueous infiltrations from the surface 

 penetrated into the thickening external zone, while at the same 

 time the successive seas piled up layer upon layer of sediments, 

 which, at first saturated with water, came in time to contain 

 nothing more than "rock water." 



From this first remark it follows that the earth's crust is divided 

 into two concentric zones, passing gradually one into the other, 

 the deeper zone being as yet very hot, even incandescent at certain 

 points, while in the superposed zone the solid mineral elements 

 are associated with considerable amounts of substances volatili- 

 zable at relatively low temperatures, such as water and the 

 innumerable series of compounds which may so readily be extrac- 

 ted from fossiliferous and other strata, by subjecting them to 

 simple distillation. 



In the second place, the progressive cooling of the earth, the 

 very cause of planetary evolution, has constantly tended to dis- 

 turb the original condition of equilibrium established in the 

 solid crust forming the surface of the liquid nucleus. The proc- 

 ess bears a striking resemblance to that on which liquid ther- 

 mometers are based. These thermometers indicate the tempera- 

 ture because the volume of the liquid and the volume of the solid 

 container do not vary at the same rate. The earth may be re- 

 garded as a liquid thermometer, say a mercurial thermometer, con- 

 sisting merely of the bulb, which is exactly filled at the moment 

 of observation. The spontaneous cooling causes a contraction 

 both in the crust, corresponding to the bulb, and in the nuclear 

 mass, corresponding to the mercury. Owing to the difference in 

 physical condition, the nucleus contracts more rapidly than the 

 crust, whereupon the latter, being no longer supported by the 

 nucleus at every point, is subjected to a set of stresses, the result- 

 ant of which tends to be tangential and to produce horizontal 

 thrusts, which are by common accord regarded as the origin and 



