190 REACTION OF THE INTERIOR OP THE EARTH 



it shews the relations which subsist between the ejection 

 of various substances on the one hand, and earthquakes 

 and elevations on the other ; it classes together groups of 

 phsenomena which appear at the first glance very hetero- 

 geneous, as thermal springs, exhalations of carbonic acid gas 

 and sulphureous vapour, harmless eruptions of mud, and 

 the devastating phsenomena of active volcanoes. In a ge- 

 neral view of nature, all these phenomena are comprehended 

 under the one idea of the action of the interior of a planet 

 upon its crust and surface. Thus in the increase of 

 temperature in the interior of the Earth as we descend 

 from the surface, we recognise the germ not only of earth- 

 quakes, but of the gradual elevation of continents, and of chains 

 of mountains from extended fissures, of volcanic eruptions, 

 and of the production of very various minerals and rocks. 

 But it is not inorganic nature only which is influenced by 

 the reaction of the interior on the exterior. It is very pro- 

 bable that in an earlier state of the globe, far greater emis- 

 sions of carbonic acid gas mingled with the atmosphere, and 

 heightened the process by which plants assimilate carbon ; 

 and thus vast forests were formed, which in subsequent 

 revolutions were destroyed, and inexhaustible stores of fuel 

 (lignites and coal) were buried in the terrestrial strata then 

 forming at the surface. Nor should we overlook that the 

 destinies of men are in part dependent also on the form of 

 the outer crust of the Earth, on the direction and elevation 

 of mountain chains, and on the divisions and articulations 

 of upheaved continents. The investigating spirit is thus 

 enabled to ascend from link to link in the chain of phseno- 

 mena, to the supposed epoch of the solidification of the 

 planet, when, in its first transition from a gaseous to a 



