G15OLO0IC 1'OIUIATIONS. 
O \ 
4J i 
trical observations in places whence the chain of the Higher 
Alps or of the Andes is seen. Wo passed through the channel 
which divides the isle of Alegranza from Montana Clara, 
taking soundings the whole way; and we examined tin; 
archipelago of small islands situated northward of Lan- 
cerota. In the midst of this archipelago, which is seldom 
visited by vessels bound for Teneriffe, we were singularly 
struck with the configuration of the coasts. We thought 
ourselves transported to the Euganean mountains in the 
Vicentin, or the banks of the Rhine near Bonn, ’flic form 
of organized beings varies according to the climate, and it is 
that extreme variety which renders the _ study of the 
o-eography of plants and animals so attractive; but rocks, 
more ancient perhaps than the causes which have produced 
the difference of the climate on the globe, are the same 
in both hemispheres. The porphyrias containing vitreous 
feldspar and hornblende, the phonolitc, the greenstone, the 
amygdaloids, and the basalt, have forms almost as invariable 
as simple crystallized substances. In the Canary Islands, 
and in the mountains of Auvergne, in the Mittelgebirge in 
Bohemia, in Mexico, and on the hanks of the Ganges, the 
formation of trap is indicated by a symmetrical disposition 
of the mountains, by truncated cones, sometimes insulated, 
sometimes grouped, and by elevated plains, both extremities 
of which arc crowned by a conical rising. 
The whole western part of Laneerota, of which we had a 
near view, bears the appearance of a country recently con- 
vulsed by volcanic eruptions. Everything is black, parched, 
and stripped of vegetable mould. We distinguished, with 
our glasses, stratified basalt in thin and steeply-sloping 
strata. Several hills resembled the Monte Novo, near Naples, 
or those hillocks of scoria and ashes which the opening 
earth threw up in a single night at the foot of the volcano of 
Jorullo, in Mexico. In fact, the abbo Viera relates, that 
in 1730, more than half the island changed its appearance. 
The great volcano, which we have just mentioned, and which 
the inhabitants call the volcano of Teinanfaya, spread deso- 
lation over a most fertile and highly cultivated region : nine 
villages were entirely destroyed by the lavas. This catas- 
trophe had been preceded by a tremendous earthquake, ana 
