Summit of the Peak of Teneriffe in February 1829. 197 



The surface is a light pumice and ash, with small pieces of 

 porphyritic lava, covered on the outside with an ochrey crust, 

 forming at the bottom an angle of 35°, and gradually increasing 

 in steepness till near the top ; the angle is about 40°, which is 

 nearly the greatest slope the body can ascend without falling 

 backward. 



After forty-five minutes of considerable exertion I seated 

 myself on the highest pinnacle of the Peak, 12*188 feet above 

 the sea. Round the summit runs a wall of porphyritic lava, 

 which forms an ellipsis, having the axis from the N. W. to S.E. 

 Within is the crater, which I consider to be about 150 feet long, 

 1 00 broad, and 50 deep. I believe it is generally described to be 

 much larger ; but having only paced it, I cannot be certain 

 that this is correct. On the east side the wall is broken down, 

 apparently by an ancient eruption of lava, the remains of 

 which appear above the pumice on the ascent : the south-west 

 part has likewise given way, but it rises in a high mass towards 

 the north. The whole of the lavas were in a rapid state of 

 decomposition ; and the surface is of a chalky-white colour, pro- 

 duced no doubt by the sulphurous acid gas acting upon the 

 alumina of the lava. The sides and bottom of the crater were 

 rather hot; and from the W.N.E. to the E.N.E. there was 

 a vast number of holes, about an inch in diameter and one or 

 two feet deep, some of them emitting steam, and others sul- 

 phureous vapours, which show that they must proceed from 

 different sources, although the apertures were only a few 

 inches apart : the heat of them was considerable, as a thermo- 

 meter graduated to 133° burst when placed within their in- 

 fluence ; and a stick thrust into one of them had the bark com- 

 pletely charred. The steam when condensed was perfectly 

 tasteless, but the apertures whence the other vapours were 

 issuing, were surrounded with the finest needle-shaped crystals 

 of sulphur. In many parts of the bottom of the crater there was 

 a white sort of paste, consisting of silica and alumina; a ther- 

 mometer placed upon it rose to 107°. 



As the plain of the Cafiadas, upon which the Peak is si- 

 tuated, rises by degrees to the elevation of nearly 9000 feet, 

 you are not aware of the great height of this volcano till you 

 are on its summit. The clearness of the atmosphere even in 

 the valleys below surpasses that of Italy, and no doubt equals 

 the cloudless sky of most of the Pacific isles; but it is greatly 

 exceeded on the top of the Peak, where on a clear day the eye 

 is able to take in the enormous extent of between five and six 

 thousand square leagues of vision. This peculiar clearness of 

 the atmosphere is probably caused by the great dryness of the 



air 



