DOMAIN II. SILICEOUS. 



STRUCTURE II, ARGILLACEOUS. 



This rock is more often the product of decom- 

 position, which changes the felspar into clay. 



Argillaceous granite, with quartz, mica, and 

 martial clay, from Hungary and Sweden. 



STRUCTURE III. TALCOUS. 



From this division talc, and even steatite, must 

 be excluded, as being often mere modifications or 

 decompositions of mica. 



Granitoid of felspar, quartz, and serpentine, 

 from Transylvania* 



MODE X. GRANITIC PORPHYROID. 



Description, In this substance, which is very frequent in 

 nature, some large or distinct crystals of felspar 

 are sprinkled on a base of granitin; and the 

 base being here assumed as the only ground of 

 classification of the substances vaguely called 

 porphyries, it must of course fall into this divi- 

 sion. The base may consist of quartz, felspar, 

 and siderite; or quartz, felspar, and mica; or 

 even any two of these substances. Some of the 



