180 



potash necessary to the formation of alum is 

 found not only in feldspar, mica, pumice stone, 

 and augit, but also in obsidians *. This last 

 substance is very common at TenerifFe, where it 

 forms the basis of the tephrinic lava *f. These 

 analogies between the Peak of TenerifFe and the 

 Solfatara of Puzzuoli, would no doubt appear 

 more numerous, if the former were more ac- 

 cessible, and had been frequently visited by na- 

 turalists. 



An expedition to the summit of the volcano 

 of TenerifFe, is interesting, not solely on account 

 of the great number of phenomena which are the 

 objects of scientific research ; it has still greater 

 attractions from the picturesque beauties, which 

 it lays open to those who are feelingly alive to 

 the majesty of nature. It is a difficult task, to 

 describe those sensations, which act with so 

 much the more force as they have something un- 

 defined, produced by the immensity of the space 

 as well as by the greatness, the novelty, and the 

 multitude of the objects, amidst which we find 

 ourselves transported. When a traveller at- 

 tempts to furnish descriptions of the loftiest 

 summits of the globe, the cataracts of the great 

 rivers, the tortuous vallies of the Andes, he is 



* Collet Descotils, in the Ann. de Chimie, t. liii, p. 260. 

 See Klaproth Beitrage, B. 5, p. 159, 162, and 166. 



t Lam^thiere, Mine>alogie, t. ii, p. 533 > and Journal de 

 Physique, 1806, p. 192. 



