236 INTERACTION OF NATUEAL FORCES. 



with space, and that the unformed earth, and the waters of 

 the great deep, which were afterwards divided into waters 

 above the firmament, and waters below the firmament, resem- 

 bled the chaotic components of the world. 



Our earth bears still the unmistakable traces of its old 

 fiery fluid condition. The granite formations of her moun- 

 tains exhibit a structure, which can only be produced by the 

 crystallization of fused masses. Investigation still shows 

 that the temperature in mines, and borings, increases as we 

 descend ; and if this increase is uniform, at the depth of fifty 

 miles, a heat exists sufficient to fuse all our minerals. Even 

 now our volcanoes project, from time to time, mighty masses 

 of fused rocks from their interior, as a testimony of the heat 

 which exists there. But the cooled crust of the earth has 

 already become so thick, that, as may be shown by calcula- 

 tions of its conductive power, the heat coming to the surface 

 from within, in comparison with that reaching the earth from 

 the sun, is exceedingly small, and increases the temperature 

 of the surface only about one thirtieth of a degree centigrade ; 

 so that the remnant of the old store of force which is enclosed 

 as heat within the bowels of the earth, has a sensible influence 

 upon the processes at the earth's surface, only through the 

 instrumentality of volcanic phenomena. These processes owe 

 their power almost wholly to the action of other heavenly bodies, 

 particularly to the light and heat of the sun, and partly also, 

 in the case of the tides, to the attraction of the sun and moon. 



Most varied and numerous are the changes which we owe 

 to the light and heat of the sun. The sun heats our atmos- 

 phere irregularly, the warm rarefied air ascends, while fresh 

 cool air flows from the sides to supply its place : in this way 

 winds are generated. This action is most powerful at the 

 equator, the warm air of which incessantly flows in the upper 

 regions of the atmosphere towards the poles : while just as 

 persistently, at the earth's surface, the trade wind carries new 

 and cool air to the equator. Without the heat of the sun all 



