DOMAIN III. ARGILLACEOUS. 



grauwack, sand-stone, &c. form extensive re- 

 gions of the earth. 



* 



STRUCTURE I. ARGILLACEOUS INTRITE, WITH CRYSTALS 

 OF FELSPAR. 



This substance forms large mountains in Lower 

 Hungary, and sometimes contains chalcedonies, 

 carnelians, amethysts, or zeolite *. According to 

 Werner it is either primary or secondary; the 

 latter containing branches and roots, and even en- 

 tire trees, petrified ; as, for example, near Chem- 

 nitz in Saxony. The primitive argillaceous por- 

 phyry has commonly a red base, but differing 

 much in hardness from genuine porphyry. 



This intrite forms a considerable portion of the 

 Andes, and of the metallic mountains of New 

 Spain. The saxum metalliferum of Baron Born 

 is also a clay porphyry, but is justly classed 

 among the Decomposed Rocks. Great confusion 

 has arisen, as has already been observed, from 

 arranging the porphyries in one family ; while they 

 ought to be classed as intrites, according to their 

 various bases. 



Clay porphyry, from the metallic mountains of 

 New Spain. 



* Kirwan Geol. Ess, 206, 207. 



