20 Teneriffe. | Jan., 
42°, which is nearly the greatest angle the body can ascend in 
walking without falling backward. The pumice and ashes gaye 
way under my feet, and often caused me to slide back many yards 
before it was possible to stop myself, then I was arrested by some 
of the protruding pieces of porphyritic lava. In forty minutes after 
leaving the Rembleta, I seated myself on the highest pinnacle of 
the Peak, 12,200 feet above the level of the sea. 
The Peak is a solfatara, that is (see Plate II.), a half-extin- 
guished volcano The crater is much smaller and more shallow 
than I expected ; round the summit runs a wall of porphy- 
ritic lava of an elliptical form, about 150 feet long, 100 broad, 
and 50 deep; the surface of the lava was coated with a soft 
white mass like dough, caused by the sulphurous acid vapours 
having acted upon the argil of the lava, and turned it into a 
sulphate of alumina. As I only paced the crater once for the 
purpose of measuring it, I am not certain that the dimensions I 
have given are perfectly correct. The bottom of the crater was 
unpleasantly hot, and the air so filled with vapours of sulphurous 
acid that I was continually sneezing, and the lungs felt sore and 
pained. The surface was covered with most beautiful trimetric 
crystals of sulphur, some of a yellowish white, others of a reddish 
and greenish colour. In some little caves, only a few feet deep, 
were some small apertures covered with splendid crystals of 
octahedral sulphur; on breaking some of them, I found in the 
interior a glistening white substance something like opal, only 
that it had a crystallme structure; on my return to England 
it was analyzed, and found to contain 91 per cent. of silex, and 
the rest water. The pasty substance on the surface of the lava, 
proved to be sulphate of alumina, muriate of ammonia, and a small 
quantity (0°5 per cent.) of sulphate of ammonia. Round the 
walls of the crater were several small apertures, like small pipes, 
about an inch in diameter, some of which were emitting steam, and 
others sulphurous acid vapours, which show that they must have 
proceeded from different sources, although some of the holes were 
only a few inches apart. The heat of the steam was considerable, 
for when I placed a thermometer graduated to 135° within their 
influence, the bulb burst. 
The extreme dryness of the atmosphere and the radiation of 
the sun’s rays were distressing; the lips cracked; the nails became 
brittle; the mahogany box, containing a Daniell’s hygrometer, 
became unglued, and the case of a small pocket-sextant split across. 
The evaporation of the wet-bulb thermometer was so rapid that it 
was necessary to watch it closely, otherwise the muslin would be 
dry before the observation could be made. 
The basaltic lava and the trachytes of the Peak were magnetic 
and had polarity, but I had no means of measuring it. 
