219 



general the farther we go back from the period 

 of modern eruptions, the more appearance the 

 currents, increasing both in size and extent, ac- 

 quire of real rocks, in the regularity of their po- 

 sition, in their division into parallel strata, or in 

 their independence of the present form of the 

 ground. 



The Peak of Teneriffe is, next to Lipari, the 

 volcano that has produced most obsidian. This 

 abundance is so much the more striking, as in 

 other regions of the Earth, in Iceland, in Hun- 

 gary, in Mexico, and in the kingdom of Quito, 

 we meet with obsidian only at great distances 

 from burning volcanoes. Sometimes they are 

 scattered over the fields in angular pieces, for 

 instance, near Popayan, in South America ; at 

 other times they form isolated rocks, as at 

 Quinche, near Quito ; in other places, and this 

 position is very remarkable, they are dissemin- 

 ated in perlstein, as at Cinapecuaro, in the pro- 

 vince of Mechoacan*, and at Cabo de Gates, 

 in Spain. At the Peak of Teneriffe, the obsi- 

 dian is not found toward the basis of the vol- 

 cano, which is covered with modern lava : it is 

 frequent only toward the summit, especially from 

 the plain of Retama, where very fine specimens 

 may be collected. This peculiar position, and 

 the circumstance that the obsidian of the Peak 

 has been ejected by a crater, which for ages 



* To the west of the city of Mexico. 



