354 ARGILLACEOUS SCHIST. 



other matters will find a more appropriate place 

 in . the synopsis, where the unessential minerals 

 are also enumerated. 



The last circumstance of importance in the 

 general character of the argillaceous schists is, 

 that they sometimes contain organic remains, and 

 even in considerable abundance. These are, 

 however, much more limited in variety than 

 those which occur in the secondary class; but 

 the species have not yet been enumerated or in- 

 vestigated. In a geological view they are highly 

 interesting. 



SYNOPSIS *OF ARGILLACEOUS SCHIST. 



FIRST DIVISION. 



Simple : of indurated schistose clay alone. 



A. Straight fissile, or continuously laminar. 



a. With a straight even fracture on the sur- 



face of the lamina. 



b. With a rough or undulated fracture. 



