38 DOMAIN VIII. DIAMICTONIC. 



combinations; while those of calcareous 

 earth and magnesia are far more rare. In 

 his Geological Essays he observes, that 

 stones are either original, as granite, or de- 

 rivative, as sand-stone ; while, in his mine- 

 ralogy, he has classed sand-stone, along 

 with granite, among the aggregates. 



The appellation and distinction are in 

 fact alike fallacious. That a red sand- 

 stone may be derived from the detritus of 

 a red granite, may be justly admitted; but 

 this affords almost the only example of a 

 real derivative stone. And the intimate 

 combinations of which Mr. Kirwan speaks 

 are so far from being derivative, that they 

 often belong to the most original and pri- 

 mitive substances. But when Mr. Kirwan 

 published his valuable system in 1794 (and 

 the last edition is merely reprinted), the 

 knowledge of rocks was extremely con- 

 fined, and regarded only as an appendage 

 to mineralogy, instead of forming a grand 

 and distinct science, a rank to which its 

 dignity and importance authorise it to 

 aspire. 



