216 COSMOS. 



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

 bon which was not taken up by alkaline earths, but remained 

 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 orga- 

 nization of animal life. Abundant eruptions of sulphurous 

 vapour have occasioned the destruction of the species of 

 mollusca and fish which inhabited the inland waters of the 

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

 torted beds of gypsum, which have doubtless been frequently 

 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.f All these substances 

 owe their 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 in- 

 creases with the depth of the strata with which they are in 

 contact at their origin. We have already spoken of the 

 numerical law regulating 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 

 difficult to determine the position of the Isogeothermal lines^ 

 (lines of equal internal terrestrial temperature), when this 

 determination is to be made from the temperature of flowing 

 springs. Such at any rate is the result I have arrived at from 

 my own observations and those of my fellow travellers in 

 Northern Asia. The temperature of springs, which has become 

 the subject of such continuous physical investigation during 



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



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



On the theory of isogeothermal (chthonisothermal) lines, consul* 

 the ingenious labours of Kupffer, in Fogg. Annalen, bd. xv. s. 184, and 

 bd. xxxii. s. 270, in the Voyage dans VOural, pp. 382-398, and in the 

 Edinburgh Journal of Science, New Series, vol. iv. p. 355. See also 

 Kamtz, Lehrb. der Meteor., bd. ii. s. 217 ; and, on the ascent of the 

 chthonisothermal lines in mountainous districts, Bischof, s. 174-198. 



