5*2 CANARY ISLANDS. 



blocks of feldspathic lava with a base of pyroxene, and con- 

 tains crystals of feldspar ; and in some instances are found 

 fragments of granitic lava. 



The present crater of this volcano, called by the Span- 

 iards, la c alder a, is of an elliptical form, surrounded by a 

 wall of lithoidal lava, shelving down on each side, and 

 forms a hollow like a vast amphitheatre. It inclines to the 

 S.S.E. at an angle of about 15°, having a tranverse diameter 

 of 420 feet, a conjugate diameter of 350, and a depth of 

 103 feet. There is continually rising from the small 

 crevices, an aqueous vapor which issues with such force, 

 as to create a peculiar buzzing noise. It condenses against 

 the neighboring walls, and distils in drops of sulphuric, or 

 muriatic acid, while the residue adheres to the rocks, and 

 forms an incrustation of fine crystals of sulphur. It also 

 acts on the scattered fragments of lava about the crater, 

 and forms certain portions of it into a soft, whitish paste, in 

 which, are found crystals of sulphate of alumine. 



This volcano may be compared to a grand laboratory 

 for manufacturing sulphuric acid. There probably exists 

 an extensive bed of ignited sulphur, deep in the earth, and 

 by large quantities of nitre, or some other substance, it is 

 supplied with oxygen to maintain its combustion. And as 

 the mountain is constantly absorbing moisture from the rain, 

 clouds and snows, which prevent the escape of the volatile 

 matter, by imbibing the sulphureous vapors, it gradually 

 becomes more and more acid, till it exudes in the man- 

 ner above described. 



An expedition to the summit of this mountain is particu- 

 larly interesting, on account of the multiplicity of phe- 

 nomena, which are objects of scientific investigation, and 

 still it has great attractions from its picturesque beauties ; 

 but I never could recommend a person to subject himself to 

 all the toils and fatigues in accomplishing it, on account of 

 the latter, for he will surely return, like almost every one, 

 dissatisfied. 



Port Orotava, Friday, ) 

 September 13, 1833. \ 



