176 



DOMAIN II. SILICEOUS. 



exaggeration to say, that this mountain alone is ca- 

 pable of providing, for a long succession of years 

 to come, all Europe with sufficient soda; pre- 

 supposing, however, that expedients should be 

 devised to separate this alkali from the stone by a 

 cheap and profitable method*." 



STRUCTURE III. EARTHY. 



This is described by Saussure as of an earthy 

 or granular appearance, with long and irregular 

 crystals of black siderite, sometimes greenish. 

 The rock was mistaken for a sand-stone. He also 

 mentions, 1 1 36, a rock of a violet red, which he 

 conceives to consist of the earth of felspar not 

 crystallised. 



Earthy klingstein-porphyry, from Mont Dor, 

 described by Daubuisson in his account of the 

 basalts of Auvergne. 



The following varieties may also be added from 

 the former great petralogist : 



Rocks of felsite, with veins which at first might 

 be taken for granite, but upon examination is 

 found to present only felspar and mica, and some- 

 times only felspar confusedly crystallised. Sauss. 

 1194. 



