213 



We have already observed, that from the le- 

 vel of the sea to Portillo, and as far as the en- 

 trance on the elevated plain of the Retama, 

 that is two thirds of the total height of the vol- 

 cano, the ground is so covered with plants, that 

 it is difficult to make geological observations. 

 The currents of lava, which we discover on the 

 slope of Monte Verde, between the beautiful 

 spring of Dornajito and Caravela, are black 

 masses, altered by decomposition, sometimes 

 porous, and with very oblong pores. The basis 

 of these lower lavas is rather wacke than basalt - y 

 when it is spongy, it resembles the amygda - 

 loids # of Frankfort on the Main. It's fracture 

 is generally irregular ; wherever it is conchoidal, 

 we may presume, that the cooling was more 

 rapid, and the mass was exposed to a less pow- 

 erful pressure. These currents of lava are not 

 divided into regular prisms, but into very thin 

 layers, not very regular in their inclination 5 

 they contain much olivine, small grains of mag- 

 netic iron, and augits, the color of which often 

 varies from a deep leek green to an olive green, 

 and which might be mistaken for crystallized 

 olivine, though no transition from one to the 

 other of these substances exists f. Hornblende* 



* Wakkenar tiger mandelstein of Steinkaute. 

 f Steffens, Handbuch der Oryktognosie, T. i, s. 304. The 

 crystals which Mr. Friesleben and myself have made known 

 under the denomination of foliated olivine (blcettriger olivinj 



