358 ARGILLACEOUS SCHIST. 



Some varieties of a. pass into hornblende 

 schist. 



4 



E. Argillaceous schist, A. div. first intermixed 

 with quartz. 



a. An uniform arenaceous mixture of sand 



and blue clay : imperfectly schistose, and 

 somewhat resembling- an argillaceous 

 sandstone. 



Occurs in Scotland, in Seil and Luing. 



b. Quartz sand intermixed with laminar or 



massive schist. Fine graywacke, and 

 graywacke schist, of mineralogists. 



c. Quartz gravel of various sizes similarly in- 



termixed : coarse graywackes. 



It is not unusual for the gravel in each differ- 

 ent variety to preserve an average general size. 



F. Argillaceous schist, C. div. first, intermixed 

 with quartz. 



a. With very fine grains or powder of quartz. 



Not fissile ; fracture sometimes rough 

 splintery, and often resembling the fine 

 and grey varieties of primary sandstone.. 



b. With visible grains of quartz of various 



sizes and resembling the coarser varieties 

 of the same rock. 



This is also termed graywacke by mine- 

 ralogists. 



