272 MICACEOUS SCHIST. 



which, in most other particulars, it so strongly 

 resembles. 



It is a theoretical question whether this tex- 

 ture is the result of chemical action or of mecha- 

 nical disposition, and therefore not adapted to v 

 the present work. But it may briefly be re- 

 marked, that the parallel position of the mica 

 may be accounted for on either supposition ; 

 while, with respect to the quartz, it certainly, in 

 every case, even where most granular, is united 

 by the intervention of a crystalline cement of the 

 same substance. 



Nevertheless, certain varieties of micaceous 

 schist occur, which possess the unquestionable 

 characters of a compound, at least partly mecha- 

 nical. In these, fragments of granite, of quartz 

 rock, and of limestone, are imbedded in the ge- 

 neral mass ; resembling, thus, the conglomerates 

 which accompany the sandstones. 



Moreover, in certain places in Scotland, 

 where small beds of micaceous schist alternate 

 Avith clay slate and gray wacke, or with coarse 

 and fine argillaceous schists, some remarkable 



