PREFACE. 

No two mountains of the Western Hemisphere have been per- 
haps longer or more widely known than those treated of in the fol- 
lowing pages. First brought into notice in 1519 by Cortes during 
his conquest of Mexico, they have been more or less identified with 
many subsequent events, not only of Mexican but also of our own 
history. This is largely for the reason that the pass between them 
has furnished the route by which American as well as Spanish and 
French invaders have marched to the beautiful Capital. 
Tourists and travelers have for centuries been drawn to them too, 
on account of the majestic and striking appearance which they present 
as seen from the City of Mexico, to whose scenic charms they lend an 
imposing and beautiful background. 
Popocatepetl has, moreover, to many generations of school 
children, been known as a volcano usually mentioned by their geog- 
raphies, which had a name so formidable that it stuck in their 
memories, like a burr, after less prickly terms had disappeared. Yet, 
in spite of the long-continued interest to which these mountains may 
lay claim, any detailed account in English of their history or geology 
is hard to find. Spanish and German explorers have described them 
in more detail, but with the exception of Sonntag, few English writers 
have sought to give any scientific description of them. This fact 
tempts one to quote the remark of a distinguished geographer, that 
‘«the English are the first to explore but the last to describe.” 
My own opportunity for observing the features of these moun- 
tains was indeed brief, so brief that were wider knowledge of them 
extant I might well hesitate to give my own observations publication. 
At the same time impressions were gained which deserve some weight 
when taken in connection with the opinions of other observers; experi- 
ence valuable for further work was obtained, and the opportunity 
afforded to study somewhat more in detail than other observers have 
done the glacier on Ixtaccihuatl enables me to add something to the 
meager fund of knowledge possessed in regard to tropical glaciers. 
Deeming my own observations, therefore, not unworthy of: publica- 
tion, I have thought that to join with them a résumé of what other 
observers, chiefly Spanish and German, had noted, would put the 
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