DOMAIN III. ARGILLACEOUS. 



Lustre, dull, sometimes faintly glimmering. 

 Opake. 



The usual colour is grey, sometimes approach- 

 ing to black. It may also be brownish, from 

 iron ochre. Wacken sometimes contains mica, 

 but this mixture cannot be regarded as charac-* 

 teristic, as appears from the amygdalites. 



Wacken is ranked by the German mineral- 

 ogists as intermediate between basalt and clay. 

 Like basalt it sometimes presents siderite, but 

 never contains augite or olivine. It is regarded 

 as secondary, because petrified wood has been 

 found in it : but such arguments are sometimes 

 fallacious, for the detritus of a primitive rock 

 may again consolidate, as in the case of granite, 

 and it is easily conceivable that it may thus en- 

 velope substances foreign to its original form- 

 ation. 



Wacken is often a corn&enne, or roche de corne, 

 of the French mineralogists. The grauwack of 

 the Germans is a very different substance, which 

 will be described among the Argillaceous Glu- 

 tenites. 



Wacken, from Saxony, &c 



