Studies for Students, 



THE PRINCIPLES OF ROCK WEATHERING. 



1. Preliminaiy generalities. 



2. Agencies engaged in Promoting Rock weathering. 



(a) Action of the Atmosphere. 

 {b) Chemical Action of Water. 

 {c) Mechanical Action of Water and of Ice. 



3. Analyses of Fresh and Decomposed Rocks. 



4. Discussion of Results and Resume. 



(1) PRELIMINARY GENERALITIES. 



In the series of papers to be given under the above title it 

 is proposed to discuss briefly the principles involved in the 

 breaking down of rock-masses when subjected to the ever vary- 

 ing conditions commonly grouped under the name of " weath- 

 ering." 



So striking a phenomenon as the disintegration of a mass of 

 firm rock, naturally did not escape the observation of the earlier 

 workers in geology, and the older literature, from the time of 

 Hutton, bears numerous references to it, though the full signifi- 

 cance of atmospheric agencies in bringing about the result, seems 

 not at first to have been fully realized. Indeed the earliest satis- 

 factory accounts to which we have access, are those of writers of 

 the present century, which are based largely upon observations 

 made in moist and warm climates, where the results of such 

 weathering are most apparent. 



The exciting cause of this decreneration has been a matter of 



O O 



considerable speculation, and, before proceeding further, it may 

 be well to indicate in brief their tendencies. 



Fournet, as quoted elsewhere, writing as early as 1833, 

 insisted upon the efficacy of water containing carbonic acid in 



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