ROCA DEL OESTE. 35 
Exposed to the sun’s rays the thermometer rose in 
the former to 124-2°, and in the latter to 104°; 
while in the shade the temperature of the air was 
81-5°, being 14° higher than the seaair. The quartzy 
sand contains fragments of felspar. Pieces of gra- 
nite have been observed at Teneriffe ; and the island 
of Gomera, according to M. Broussonet, contains a 
nucleus of mica-slate. From these facts Humboldt 
infers that, in the Canaries, as in the Andes of Qui- 
to, in Auvergne, Greece, and most parts of the globe, 
the subterranean fires have made their way through 
primitive rocks. 
Having re-embarked, they hoisted sail, and en- 
deavoured to get out again by the strait which se- 
parates Alegranza from Montana Clara; but, the 
wind having fallen, the currents drove them close 
upon a rock marked in old charts by the name of 
Infierno, and in modern ones under that of Roca del 
Oeste,—a basaltic mass which has probably been 
raised by volcanic agency. ‘T'acking during the night 
between Montana Clara and this islet, they were 
several times in great danger among shelves towards 
which they were drawn by the motion of the water ; 
but the wind freshening in the morning, they suc- 
ceeded in passing the channel, and sailed along the 
coasts of Lancerota, Lobos, and Forteventura. 
The haziness of the atmosphere prevented them 
from seeing the Peak of Teneriffe during the whole 
of their passage from Lancerota; but our traveller, 
in his narrative, states the following interesting cir- 
cumstances relative to the distance at which moun- 
tains may be seen. If the height of the Peak, 
he says, is 12,162 feet, as indicated by the last 
trigonometrical measurement of Borda, its summit 
