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 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 beea 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, t he 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 JLam^thiere, Mineralogie, t. ii, p. 538 ; and Journal de 

 Physique, 1806, p. 192. 



