Dr. MacCullocho« Quartz RocL 48*7 



ancient division of primary and secondary, as far at least as relates 

 to those rocks which bear marks, however obscure, of stratification. 

 It will be a separate consideration by what means we can divide 

 those of the former class which contain organic remains, from 

 those which are without them ; a distinction, perhaps not" less 

 requisite in the one than in the other of these two leading classes, 

 since, however many members of the floetz or secondary division 

 may be characterized by the existence of these remains, a certain 

 set are as invariably free from them. 



It is perhaps beyond the bounds of the present notice, to suggest 

 the propriety of separating the unstratified rocks, such as granite, 

 porphyry, and trap, from this two-fold arrangement. Should such 

 a mea&ure be ultimately adopted, it will be further necessary to 

 consider how far any one of the several unstratified rocks is peculiar 

 to the one set of stratified ones, and how far it is common to both.. 

 A more accurate knowledge of the various rocks designated under 

 the loose name of porphyry, will be particularly requisite to the 

 forming of this arrangement. 



