28 C A N A R Y I S L A N D S . 



agreeable contrast with the dark stones and earth upon 

 which it usually grows. 



All the shores and ravines in this vicinity are lined with 

 basalts and other igneous rocks, in which may be found 

 crystals of hornblende, and in some instances, olivine and 

 transparent pyroxene, the latter occurring generally, in 

 six-sided prisms, and of an olive-green tint. I observed, 

 also, large quantities of volcanic sand along the shore, con- 

 taining minute fragments of the same materials as the 

 neighboring rocks are composed. From the reverberation 

 of this sand, and the black, arid rocks with which the 

 shores of this island are formed, may be imputed the 

 intense heat to which they are exposed. This sand, in the 

 middle of a hot day, is insupportable to the hands or bare 

 feet for any length of time. 



From the hazy state of the atmosphere, we did not dis- 

 cern the Peak before the 9th instant, at mid-day, which 

 was then at sixty miles' distance. When it first came un- 

 der our observation, the horizon below it, as far as the eye 

 could reach, exhibited only a wide expanse of water, so 

 that the summit appeared like a thin blue vapor, till its 

 stationary position fixed our attention. It was soon con- 

 cealed from view, and was seen no more until half past 

 three in the afternoon, when its conical head was tower- 

 ing far above the clouds. I now availed myself of making 

 a trigonometrical measurement of its height, which I did 

 by throwing the log, and noting the velocity of the vessel, 

 and the time it sailed between two stations, to determine 

 a base ; and employed two vertical angles of the summit of 

 the Peak, one at each station. By my calculation I found 

 it to be elevated 1-2,352 feet above the ocean, which is 

 considerably more than the average measurements that 

 have been made by different observers, showing at once 

 the uncertainty of this mode of measurement of mountains. 



For want of other matters of interest, I may here take a 

 glance of the physical observations since my departure, 

 relating to the air and the ocean, with some remarks from 

 other sources. 



Temperature of the Air. — The great basin of the 

 Northern Atlantic Ocean, between Europe, Africa, and 



