190 



With respect to the argillaceous schists, it is 

 only necessary to mention two more of the asso- 

 ciations and transitions which they display. The 

 finer kinds sometimes pass into chlorite schist 

 where they occur in company with that rock. 

 The coarser often alternate with the primary 

 sandstone ; and they pass into it by a gradual in- 

 crease of the quartz, and a loss of the clay, in 

 their composition. 



The last transitions in the primary class that 

 remain to be noticed, are those of serpentine. 

 This rock is occasionally associated with horn- 

 blende schist, in which case it sometimes passes 

 into that rock by an imperceptible gradation. 

 It seems also, in some rare instances, to pass 

 into the basalt or greenstone of the overlying* 

 family ; a transition which, perhaps, would have 

 been more properly described in the secondary 

 class. 



The very limited number of the rocks that 

 belong to the secondary class, leaves but little to 

 say on the subject of the transitions which occur 

 among them. 



