Classifications of Rocks. 



49 



ARTIFICIAL SYSTEM. 



NATURAL 

 SYSTEM. 



ALLUVIAL CLASS. 



Marine, elevated; loose. Italy, containing marine 

 remains. 

 „ „ indurated. Marl of Italy. 



Coral. Islands of Pacific, &c. 



Terrestrial, loose, of very various materials. 



„ general, of diluvian origin, or else elevated 

 and marine. 



„ local, from transportation ; and from de- 

 composition. 



,, soil. 



„ solid, Travertino, of Italy. 



„ „ West Indian and Coral sandstones. 



Messina and others. 



„ „ Marl of lakes. 



»» „ Peat. 



class 8. 



CLASS 9. 



VOLCANIC CLASS, 



CLASS 10. 



Lava 



} Presenting, under these general 

 terms, analogies to many of the 

 trap-rocks. 



I know not that I have much to remark on the preceding 

 table, which the reader who is versed in geology may not re- 

 mark for himself. 



The repetitions of the same rocks in the different classes 

 became a matter of course in a classification of this nature. 



I have attempted to distinguish some porphyries as ex- 

 clusively belonging to the primary class ; as is unquestionably 

 the fact. 



In the 5th class, I have given only the principal varieties of 

 the different rocks. To form a classification on the basis of 

 the English strata, would be to prejudge a question of which 

 we know not as yet enough, and to commit again an error from 

 which geology has already severely suffered. 



To distinguish more minutely in the secondary or tertiary 

 classes, would be to introduce a new and insufferable arrange- 

 ment; because the same principle must also extend to the 

 primary, giving us three or four kinds of gneiss, of quartz rock, 

 and so on. Important as particular strata may seem in an 

 English or any other series, it must be remembered that they 

 are still but varieties, in the general system. 



JULY— sept., 1829. E 



