358 



INFLUENCE OF INTERNAL FORCES. 



CHAPTER 

 XXVIIL 



Traces in 

 Europe and 

 Asia. 



Elucidation 

 ot pvobleiiis 

 iu science. 



Opflratinn of 



internaj 



forces. 



Previous 

 aotiuuii. 



tween the "Wolga and the Jaik. The depression of a mass 

 of continent 80 feet below the surface of the waters of 

 the ocean, in tlieir mean state of equilibrium, has never 

 been considered in all its importance, because we are ig- 

 norant of the extent of this depression, of which some 

 parts of the coasts of Europe and Egypt (in Holland, and 

 at the Natron lakes) present only feeble traces." 



This intimate connexion between these diversified ap- 

 pearances is now serving to elucidate many problems in 

 geology and physics which had previously been consid- 

 ered inexplicable. Tlie analogies of observed facts, and 

 the strict investigation of phenomena of recent occur- 

 rence, gradually lead us to more probable conjectures as 

 to the events of those remote j)eriods which preceded his- 

 torical records. The influence which the forces in the 

 interior of our planet exercise upon its external envelope 

 in the various stages of its refrigeration, on account of the 

 unequal aggregation in which its component substances 

 occur, is at the present day in a very diminished condi- 

 tion. These forces appear now to be restricted to a small 

 number of points ; intermittent ; simplified in their 

 chemical effects ; producing rocks only around small 

 circular apertures, or over longitudinal cracks of small 

 extent ; and manifesting their power, at great distances, 

 only dynamically, by shaking the crust of our planet in 

 linear directions, or in spaces which remain the same 

 during a great number of ages. Previous to the existence 

 of the human race, the action of the interior of the globe 

 upon the solid crust, which was increasing in volume, 

 must have modified tlie temperature of the atmosphere, 

 and rendered the whole surface capable of giving birth to 

 those i)roductions which are now regarded as exclusively 

 tropical . since that time, by the ett'ect of the radiation 

 and refrigeration of the exterior, the relations of the earth 

 to a central body, the sun, began almost exclusively to 

 determine the diversity of geographical latitudes, and to 

 give their present character to the various climates of 

 the earth's zones. 



