362 ARGILLACEOUS SCHIST. 



mens, would consist in the sizes of the fragments, 

 and the consequent coarse texture of the rocks. 



It must be remarked, that many instances 

 occur, in which specimens of these argillaceous 

 schists are undistinguishable from shales, as ob- 

 served also under that head. The distinction can 

 only be made, in such cases, by reference to the 

 geological connections. 



The following minerals occur imbedded in 

 argillaceous schist, and most commonly in the 

 simple and fine varieties. 



Wavellite. Stilbite. 



Chiastolite. Tremolite. 



Staurotide. Cyanite. 



Andalusite. Topaz. 



Brown spar. Lazulite. 



Calcareous spar. Opal. 



Chlorite. Pyrite*. 



Garnet. Oxydulous Iron. 

 Epidote. 



In certain argillaceous schists of this division, 

 pyrites occurs in such abundance, and of such a 

 composition, that they form aluminous efflores- 

 cences on exposure to air and moisture ; pro- 

 ducing aluminous slate. The same substance 

 occurs also among the shales. 



