150 



clivities, the springs indicate too great a decre- 

 ment of caloric, because they unite small cur- 

 rents of water, which filter at different heights, 

 and their temperature is consequently the mean 

 between the temperature of these currents. The 

 spring of Dornajito has considerable reputation 

 in the country ; and was the only one known, at 

 the time of my excursion, on the road which 

 leads to the summit of the volcano. The form- 

 ation of springs demands a certain regularity in 

 the direction and inclination of the strata. On 

 a volcanic soil, porous and splintered rocks ab- 

 sorb the rain waters, and lead them to consider- 

 able depths. Hence arises that aridity observed 

 in the greater part of the Canary islands, not- 

 withstanding the considerable height of their 

 mountains, and the mass of clouds which navi- 

 gators behold incessantly piled over this archi- 

 pelago. 



From Pino del Dornajito to the crater of the 

 volcano we continued to ascend without crossing 

 a single valley ; for the same ravines (barancos) 

 do not merit this name. To the eyes of the 

 geologist the whole of the isle of TenerifFe is but 

 one mountain, the almost elliptical base of which 

 is prolonged to the north-east, and in which we 

 distinguish several systems of volcanic rocks 

 formed at different epochas. The Chahorra, or 

 Montana Colorada, and the Urea, considered in 

 the country as insulated volcanoes, are only lit- 



