72 



division here adopted. In the further progress 

 of this science, when some absolute character- 

 istics shall be discovered, it will be easy to restore 

 to the first class, and to a place in the first sub- 

 division of that class, the porphyries that are now 

 peculiarly connected with the primary strata ; 

 should it be proved that they are of an origin 

 prior to the secondary. 



As it is scarcely possible to explain these 

 views without a glance, at least, at the origin of 

 rocks, it must here be remarked, that the preced- 

 ing sketch of the supposed originally universal 

 extent of the secondary unstratified rocks, is an 

 assumption for the sake of elucidating the present 

 arrangement. There is no doubt that these rocks 

 are rather partial than general ; but that fact 

 does not alter the principal views here held out. 

 Partial depositions at a recent period, would ad- 

 mit of the same train of reasoning to a great ex- 

 tent. The only doubt which arises is, whether 

 such partial depositions may not have taken place 

 at very distinct periods. If they have occurred 

 at any time, before the formation of the secondary 



