a.EOLOai or the peak. 
97 
lava, the basis of which is obsidian, pitch-stone, and phono- 
hte. This phenomenon is the more remarkable, inasmuch as 
m . Bohemia and in other parts of Europe, the porphyrschiefer 
with base of phonolite* covers also the convex summits ©f 
basaltic mountains. 
It has already been observed, that from the level of the sea to 
I ortillo, and as far as the entrance on the elevated plain of 
the Eetama, that is, two-thirds of the total height of the 
volcano, the ground is so covered with plants, that it is diffi- 
cult to make geological observations. The currents of lava, 
which we discover on the slope of Monte Yerde, between 
the beautiful spring of Domajito 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 ; when it is spongy, it resembles 
the amygdaloidsf of Frankfort-on-tlie-Maine. Its fracture 
18 generally irregular; wherever it is couchoidal, we may 
presume that the cooling has been more rapid, and the mass 
has been exposed to a less powerful pressure. These cur- 
rents of lava are not divided into regular prisms, but into 
f Ver >' thin layers, not very regular in their inclination ; thev 
contain much olivine, small grains of magnetic iron, and 
hugite, the colour of which often varies from deep leek- 
green to olive green, and which might be mistaken for 
rystallized olivine, though uo transition from one to the 
ther of these substances exists.J Ampkibole is in general 
ery rare at Teneriffe, not only in the modem lifchoid lavas, 
cut also in the ancient basalts, as lias been observed by 
■wL. Cordier, who resided longer at the Canaries than any 
ther mineralogist. Neplieline, leucite, idocrase, and meio- 
Iwm . | ve not yet been seen at the peak of Teneriffe ; for a 
reaoish-gray lava, which we found on the slope of Monte 
, )tli rae ’ which contains small microscopic crystals, 
ppears to me to be a close mixture, of basalt and anal- 
* Klingstein. Werner, 
t V akkeuartiger mandelstein. Sleinkautc. 
which ' \iv en p . H j m l dbuch , der Oryktognosie, tom. i, s. 364. The crystal, 
tion nf r r t*j S an< l m yself have made known under the denomina. 
Karsten fl m 01V ' ne ^ mtir >» €r olivin) belong, according to Mr. 
- — ’ t0 tlle Pyroxene augite. Journal dcs Mines de Freiherr, 1791, 
■ 215 . 
VOX,. 
I. 
