90 
auooKOsr of tekeiuffe. 
is extremely small. Its diminutive size struck M. de Borda 
and other travellers, w ho took little interest in geological 
investigations. 
t -A-S to the nature of the rocks which compose the soil of 
1 eneriffe, we must first distinguish between productions of 
the present volcano, and the range of basaltic mountains 
which surround the Peak, and which do not rise more than 
five or six hundred toises above the level of the ocean. 
Here, as well as in Italy, Mexico, and the Cordilleras of 
Quito, the rocks of trap-iormation® are at a distance from 
the recent currents of lava; everything shows that these 
two classes of substances, though they owe their origin to 
similar phenomena, date from very different periods. It is 
important to geology not to confound the modem currents of 
lava, the heaps of basalt, green-stone, and phonolite, dis- 
persed over the primitive and secondary formations, with 
those porphyroid masses having bases of compact feldspar. t 
which perhaps have never been perfectly liquified, but which 
do not less belong to the domain of volcanoes. 
In the island of l’cneriffe, strata of tufa, puzzolana, and 
ciay, separate the range of basaltic lulls from the currents of 
recent lithoid lava, and from the eruptions of the present 
volcano. In the same manner as the eruptions of Epomeo 
in the island of Ischia, and those of Joridlo in Mexico, have 
taken place in countries covered with trappean porphyry, 
ancient basalt, and volcanic ashes, so the peak of Teyde 'has 
raised itself amidst the wrecks of submarine volcanoes. 
Notwithstanding (he difference of composition in the recent 
lavas of the Peak, there is a certain regularity of position, 
which must strike the naturalist least skilled in geognosy, 
'fhe great elevated plain of lie t am a separates the black, 
basaltic, and earthlike lava, from the vitreous and feldsparry 
* The trap-formation includes the basalts, green-stone (r/runstew) 
the trappean porphyries, the phonolites or porphyrschiefer, &c. 
+ These pctrosiliceous masses contain vitreous and often calcined 
crystals of feldspar, of amphibole, of pyroxene, a little of olivine, but 
scarcely any quartz. To this very ambiguous formation belong the 
trappean porphyries of Chimborazo and of Kiobamha in America, of the 
Duganean mountains in Italy, and of the Siebengebirge in Germany; as 
■veil as the ilomites of the Great-Sarcouy, of Puy-de-Dome, of the Fettle 
Cleirson, and of one part of the Ptiv-Chopin* in Auvergne. 
