VOLCANO POPOCATEPETL AND ITS VICINITY. 



57 



the sulphur, have placed a few boards. This place is called by them &quot;la cueva&quot; 

 (the cave), and it affords a little protection, at least, against the piercing winds and 

 the snow. Here I slept two nights, in January and February, 1857, on one of these 

 the thermometer going down as low as 11. S C. (February 9, at 4 o clock A. M.). 

 About thirty feet below &quot;la cucva&quot; is placed a rudely-constructed capstan of 

 wood, by means of which the sulphur is raised. It is also used in lowering persons 

 down the vertical part of the crater, which has here the least height, but which 

 still amounts to about 250 feet. From this point there is a magnificent view of the 

 crater, the southern and western walls of which indicate, by their shelved or terraced 

 form, that the lava must have accumulated in successive thick and irregular beds. 



FIG. 2. 



Ji.-Jt of Motion, of , Jiedi r 







SECTION OF CRATER FROM EAST TO WEST. 



The accompanying sections of the crater and the upper part of the cone may, 

 perhaps, serve to illustrate its general structure. The nucleus of the cone is 

 composed of compact lava, which, at least in the upper parts, is arranged in nearly 

 vertical beds. This has little or nothing of the light, spongy or scoriaccous 

 character of that seen in some volcanoes ; as, for instance, in the modern crater of 

 Jorullo (according to Prof. Monross), but is hard and very heavy, mostly of a dark- 

 red, or bluish-black color. These beds nowhere show a basaltic or columnar 

 structure. The nucleus of the cone is covered by a thick mantle of sand, scoria, 

 and pumice, where it is not too precipitous. 



In descending into the crater, the traveller is usually preceded by an Indian, and 

 there is some danger of being hurt by the stones which are constantly falling from 

 above him. The action of the frost is doubtless a principal agent in detaching 

 these stones. The sun shining on the snow which covers the edge of the crater, 

 and the shelves or narrow terraces, melts a part of it, the water penetrates into 

 the minute crevices of the rocks, where it freezes again, and, expanding while it 

 changes into ice, has an effect similar to that of gunpowder. 



One of the guides, who had been many times in the crater, asserted that the 

 bottom of it rises six feet annually by the accumulation of the detached stones. 

 This is certainly an exaggeration; nevertheless, the amount of rise is considerable, 

 since at least ten stones fall per hour, of more than two feet diameter, or certainly 

 more than 2000 cubic feet in a day (probably double this quantity). If now we 



