§ 19. EXISTING GEOLOGICAL AGENTS. 53 



reaching the earth in a high state of temperature, are small 

 heavenly bodies which the attraction of our planet has 

 caused to deviate from their previous path. The aspect so 

 familiar to us of these aerolites, and the analogy which their 

 composition presents to minerals contained in the crust of 

 the earth, is very striking. The inference to which they 

 point appears to me to be, that the planetary and other 

 masses were agglomerated in rings of vapour, and after- 

 wards in spheroids, under the influence of a central body ; 

 and that being originally integral parts of the same sys- 

 tem, they consist of substances chemically identical."* 



19. Existing geological agents. — Assuming then 

 that our planet, when first called into being by the fiat 

 of the Creator, was a gaseous mass, " without form and 

 void," and destined through indefinite ages to undergo mu- 

 tations which ultimately rendered it a fit abode for man 

 and the animals which are his contemporaries, we proceed 

 to investigate the nature and effects of the agencies by 

 which its surface is still modified. 



In this division of the subject it will be my object to 

 explain in a clear and familiar manner some of those 

 physical changes which, unheeded or unappreciated, are 

 taking place around us ; but which, operating on a large 

 scale, and through a long period of time, are capable of 

 producing effects that materially modify the earth's surface, 

 and give rise to results which, when viewed in the aggre- 

 gate, fill the uninformed mind with astonishment, and lead 

 it to call up imaginary convulsions and catastrophes to 

 explain the result of some of the most ordinary operations 

 of nature. As the simple lines that compose the alphabet 

 constitute, when placed in combination, the mighty engine 

 by which the master spirits of our race enlighten and 



* Cosmos ; a Sketch of a Physical Description of the Universe, by 

 Earon Humboldt ; Col. Sabine's translation. 



