F. JV. Guild — Eruptive Hocks in Mexico. 



161 



melting of the snow. The maximum depth of the crater from the 

 surface of the lake to the highest point of the rim is said to be 

 505 meters. At the malecate, or hoist, formerly used in extract- 

 ing sulphur from the crater, the depth is considerably less, being 

 but 205 meters.* The bottom of the crater contains several 

 small solfataras, from which steam and sulphur vapor escape. 

 It is impossible to enter the crater except by means of a rope 

 down a perpendicular cliff 250 feet high. The descent, how- 



Fig 1. Popocatepetl, a bank of volcanic ash projecting through the snow. 

 About 1000 ft. below the crater. 



ever, lias been made by members of the Geological Institute of 

 Mexico, who spent forty-eight hours in the crater investi- 

 gating- it.* The interior heat of the volcano is still sufficient to 

 prevent the crater becoming filled up with snow. 



The rocks of Popocatepetl f consist of andesites and basalts 

 with the usual accompanying pumiceous and scoriaceous forms, 

 which are especially well developed immediately below the snow 

 line, where many barrancas, or deep cuts, commence and radiate 

 outward, giving an excellent opportunity for studying it. One 

 of the deepest of them, the Barranca de Tlamacas, cuts through 

 this material to the depth of 200 feet or more and exposes beds 

 made up alternately of fine volcanic ash and coarse pumiceous 



* Aguilera y Ordonez, Expedicion Cien. al Popocatepetl. 



f An excellent account of an ascent of Popocatepetl, with observations upon 

 its geography and geology with a brief description of its lavas, has been given 

 bv Farrington — Geological Series of the Field Columbian Press, vol. i, 

 No. 2, 1897. . 



