199 



HORNBLENDE SCHIST. 



In this very common rock, hornblende alone, 

 or hornblende and felspar, form the necessary in- 

 gredients. The structure is not always, or neces- 

 sarily, schistose ; and it cannot be confounded 

 with any other substance, excepting as it presents 

 the transitions into gneiss, formerly described. 



ACTINOLITE SCHIST 



Is in every respect similar to the former in 

 structure ; but it is rare, and is readily distin- 

 guished from that ; as far, at least, as the essential 

 mineral is distinguishable from hornblende. 



QUARTZ ROCK. 



This consists, either of pure quartz, compact, 

 or imperfectly granular; or it is a compact 

 granular compound of quartz and felspar, or of 

 quartz and mica, subject to other accidents which 

 must be sought in the table of varieties. The 

 obviously re-united structure even of the most 

 compact kinds, together with the marks of strati- 

 fication, prevent the compounds of quartz and 



