81 



CHAP. V. 



REMARKS ON THE GENERAL CATALOGUE OF THE 

 ROCKS CONTAINED IN THIS ARRANGEMENT, 

 AND ON THE ORDER OF THEIR SUCCESSION IN 

 NATURE. 



IN the preceding general catalogue are comprised 

 all the rocks which seem to have been decidedly 

 ascertained by geologists to constitute distinct 

 massses in nature. Our knowledge is not how- 

 ever as yet sufficiently accurate or extensive to 

 enable us to determine whether all the inferior 

 varieties, here ranked under the general heads, 

 are accurately referred ; or whether some of them 

 may not have claims to distinct places in the sys- 

 tem. The chief of these doubts relate to certain 

 rocks not found in Britain, the geological connec- 

 tions of which have not been satisfactorily inves- 

 tigated or described. I may quote, as an exam- 

 ple, the topaz rock, which is here placed under 

 gneiss, from its general character. Future exa- 



G 



