GEOLOOT. 81 



sition. The degree of heat which produced the change in 

 those rocks was less intense than that which produced the 

 plutonic class, and was doubtless assisted by gaseous agency. 



We have thus given a brief outline of two systems of classi- 

 fication, without, however, giving the reasons in favor of the 

 propriety of any theory or classification. Our limits will not 

 admit of a subdivision of the classes into orders, genera and 

 species, much other useful matter must also be excluded. 

 A few of the most important rocks and the metalloids have 

 been described, being thought indispensable to a proper under- 

 standing of the principles of geology and the constitution of 

 soils. 



