GENERAL REMARKS. 



Within the last three years several ascensions have been accomplished of the 

 volcano Popocatepetl, and also two or three attempts made to reach the highest 

 point of the Ixtaccihuatl. Mr. Walker Fcarn, Secretary U. S. Legation in Mexico, 

 and Dr. Crawford, U. S. A., who ascended these mountains in January, 1857, have 

 published such excellent general descriptions of them, in different journals, that 

 little is to be added on this subject. I confine myself therefore to a geographical 

 and geological description,' and give a few notes in regard to the difficulties of 

 the ascent and the necessary precautions to be observed in the undertaking, which 

 may perhaps prove of use to travellers, hereafter attempting the exploration of 

 these or similar mountains. 



The Popocatepetl and Ixtaccihuatl are the highest peaks of a mountain ridge, 

 having a mean breadth of about fifteen and a length of forty English miles ; run- 

 ning from Lat. 18° 55' to Lat. 19° 30' N., in a direction nearly N. 10° W., at a 

 distance of thirty-five to fifty miles east of the city of Mexico. The average 

 height of the ridge is about 5000 feet above the plateau from which it rises, or 

 13,000 English feet above the level of the sea ; the Popocatepetl forms its southern 

 termination, and to the south of it the plateau also falls off — at many places 

 abruptly — several thousand feet. 



To the east of this ridge is the alluvial plain of Amecameca, 8200 feet above the 

 sea, and separated from the valley of Mexico, which is 700 feet lower, only by a low 

 ridge of volcanic origin — containing several cones with extinct craters — the height 

 of which above the plain does not exceed a thousand feet ; the waters from the 

 west side of this ridge run into the lakes, which occupy the centre of tlic valley 

 of Mexico. 



On the east side the mountains are bounded by the valley of Pucbla, which is 

 about 7500 feet above the level of the sea ; and the waters from tliis and the 

 south side run into the " Rio Mescal," a river which passes through the city of 

 Puebla and empties into the Pacific Ocean. To the north the ridge decreases 

 gradually in height until it loses itself in the plains of Apam (los llanos de Apam), 



^ I take this opportunity to express my obligations to Trof. Mouross, who kindly furnished me with 

 some valuable notes on the geology of Popocatepetl, after we ascended the volcano together in June, 1857. 



Free use of these notes has been made in the present description. 



