61 
THE SPIll.S'G OF DORXA.1ITO. 
turo of Hie coast to be 21 degrees, and allo wing one degree 
for the decrement of caloric corresponding under this zone 
to 93 toiscs. "We should not be surprised if this spring 
remained a little below the heat of the air, since it probably 
takes its source in some more elevated part of the peak, and 
possibly communicates with the small subterranean glaciers 
of which wc shall speak hereafter. The accordance just ob- 
served between the barometrical and thermometrical mea- 
sures is so much more striking, because in mountainous 
countries, with steep declivities, the springs generally indi- 
cate too great a decrement of caloric, for they unite small 
currents of water, which filtrate at different heights, and their 
temperature is consequently the mean between the tempera- 
ture of these currents. The spring of Dornajlto has con- 
siderable reputation in the country ; and at the time I was 
there, it was the only one known on the road which leads 
to the summit of the volcano. The formation of springs 
demands a certain regularity in the direction and inclination 
of the strata. On a volcanic soil, porous and splintered 
rocks absorb the ram waters, and convey them to considerable 
depths. lienee arises that aridity observed in the greater 
part of the Canary Islands, notwithstanding the considerable 
height of their mountains, and the mass of clouds which 
navigators behold incessantly overhanging this archipelago. 
From Pino del Dornajito to the crater of the volcano we 
continued to ascend without crossing a single valley; for 
the small ravines (bara)icos) do not merit this name. To the 
eye of the geologist the whole island of Teneriffo is hut one 
mountain, the almost elliptical base of which is prolonged to 
the north-east, and iu which may he distinguished several 
systems of volcanic rocks formed at different epochs. The 
Chahorra, or Montana Colorada, and the Urea, considered in 
the country as insulated volcanoes, are only little hills abut- 
ting oil the peak, and masking its pyramidal form. The great 
volcano, the lateral eruptions of which have given birth to 
vast promontories, is not however precisely in the centre ot 
the island, and this peculiarity of structure appears the less 
surprising, if we recollect that, as the learned mineralogist 
M. Cordier lias observed, it is not perhaps the small crater 
of the Piton which has been the principal agent in the 
changes undergone by the island of Teneriffo. 
