67 



In the secondary class, the stratified division 

 is placed before the unstratified, for the same rea- 

 sons that the reverse arrangement is adopted in 

 the primary. 



The rocks of this latter division, with certain 

 exceptions that do not affect this arrangement, 

 are placed above even the latest of the secondary 

 strata ; one doubtful case alone, of a partial de- 

 posit of stratified rocks, namely, that of the re- 

 cently ascertained fresh water formations, re- 

 maining for future decision. They are conse- 

 quently posterior in point of time ; although the 

 marks of that posteriority are sometimes obscure, 

 and, occasionally, wanting. But they are also 

 found in contact with the primary strata, and, as 

 before remarked, even with granite. As these 

 circumstances might be supposed to offer an ob- 

 jection to this arrangement, it is necessary to in* 

 troduce a few words on that which belongs pro- 

 perly to the general history of these rocks. 



The actual superficies of the earth offers ex- 

 amples of every rock, from granite to the last of 

 r 2 



