GASEOUS EMANATIONS. 219 



carbonic acid, vegetation must have attained a degree of vital 

 activity, and derived the superabundance of nutrition necessary 

 to furnish materials for the formation of the beds of lignite 

 (coal), constituting the inexhaustible means on which are based 

 the physical power and prosperity of nations. Such masses 

 are distributed in basins over certain parts of Europe, occur- 

 ring in large quantities in the British Islands, in Belgium, in 

 France, in the provinces of the Lower Rhine, and in Upper 

 Silesia. At the same primitive period of universal volcanic 

 activity, those enormous quantities of carbon must also have 

 escaped from the earth which are contained in limestone 

 rocks, and which, if separated from oxygen and reduced to a 

 solid form, would constitute about the eighth part of the abso- 

 lute bulk of these mountain masses.* That portion of the 

 carbon which was not taken up by alkaline earths, but re- 

 mained mixed with the atmosphere, as carbonic acid, was 

 gradually consumed by the vegetation of the earlier stages of 

 the world, so that the atmosphere, after being purified by the 

 processes of vegetable life, only retained the small quantity 

 which it now possesses, and which is not injurious to the 

 present organization of animal life. Abundant eruptions of 

 sulphurous vapor have occasioned the destruction of the spe- 

 cies of mollusca and fish which inhabited the inland waters of 

 the earlier world, and have given rise to the formation of the 

 contorted beds of gypsum, which have doubtless been fre- 

 quently affected by shocks of earthquakes. 



Gaseous and liquid fluids, mud, and molten earths, ejected 

 from the craters of volcanoes, which are themselves only a 

 kind of " intermittent springs,'' rise from the earth under pre- 

 cisely analogous physical relations.! All these substances owe 

 thoir temperature and their chemical character to the place 

 of their origin. The mean temperature of aqueous springs is 

 less than that of the air at the point whence they emerge, if 

 the water flow from a height ; but their heat increases with 

 the depth of the strata with which they are in contact at their 

 origin. We have already spoken of the numerical law regu- 

 lating this increase. The blending of waters that have come 

 from the height of a mountain with those that have sprung 

 from the depths of the earth, render it diflicult to determine 

 the position of the isogeothermal linest (lines of equal internal 



* Bischof, op. cit., s. 324, Anm. 2. 

 t Humboldt, Asie Centrale, t. i., p. 43. 



X On the theory of isogeothermal (chthonisothermal) lines, consult tha 

 ingenious labors of'Kupffer, in Pogg., Annalen, bd xv., s. 184, and bd. 



