274 MICACEOUS SCHIST. 



eluding felspar, so it easily passes into that rock 

 by the admission of this mineral. With greater 

 facility, it passes into quartz rock ; as the same 

 ingredients form one of the chief varieties of that 

 substance ; nor indeed is it often possible to de- 

 termine to which of these two, any specimen, 

 or even stratum, ought to be referred. 



As the limits between chlorite and mica are 

 evanescent, or, at least, as no effectual distinction 

 between the two has yet been discovered, mica- 

 ceous schist easily passes into chlorite schist; 

 and, although more rarely, it seems also to pass 

 into talcose schist, producing indefinite varieties 

 which are noticed in the subsequent catalogue. 

 In some rare instances also, it presents transitions, 

 but less perfect, into the finest varieties of argil- 

 laceous schist. 



Besides the essential minerals above men- 

 tioned, hornblende, chlorite, and talc, sometimes 

 occuir in micaceous schist, in such abundance as 

 materially to modify its character ; occasionally 

 producing transitions into the rocks characterized 

 by these ingredients, which it appeared conve- 

 nient to Enumerate in a particular division. 



