356 ARGILLACEOUS SCHIST. 



a. Compact, imperfectly fissile, the frag- 



ments translucent, and much resembling 

 compact felspar: common hone. 



b. Laminar or scaly ; straight or undulated, 



and the fragments translucent : also 

 used as hone. 



c. Granular, rough : less translucent, par- 



ticularly when of a dark colour. 



These varieties are frequently of a pale yel- 

 lowish, or greenish grey colour ; sometimes lead 

 blue, or the two colours occupy alternating la- 

 minae. They often weather, like compact felspar, 

 so as to display a white powdery surface, and are 

 at times not easily distinguished from some va- 

 rieties of that rock. 



D. So hard as to strike fire with considerable 

 facility ; but the particles of quartz not visible. 



This is the flinty slate or siliceous schist of 

 some authors, but it must not be confounded 

 with that which is here enumerated under the 

 head of Siliceous Schist ; which is distinct in its 

 geological position, and also distinguishable, on 

 comparison, by a peculiar aspect of compactness 

 and simplicity which cannot be described. 



