~*~! 
POPOCATEPETL AND IXTACCIHUATL—FARRINGTON, 109g 
everywhere a charm to the scene which contrasts favorably with the 
somber monotony which characterizes the route by which Popocat- 
epetl is ascended. The greater fertility of soil and the more copious 
supply of water are probably the causes which combine to give the 
slopes of Ixtaccihuatl a more abundant and varied flora than those of 
its companion. The volcanic ashes which largely cover Popocat- 
epetl both absorb the waters from the melting of the snow and 
hinder the growth of vegetation. Baker asserts* that the fauna 
and flora of the two mountains are exactly alike, but my own 
observations agree with those of Sonntag in considering the flora, 
at least of Ixtaccihuatl, to be much richer in comparison. The 
succession of zones, however, as marked by the forest growth, is 
quite similar on the two mountains. There were practically three 
of these noted, the lowest consisting of laurels, pines and cedars, the 
middle of spruces and firs, and the highest of pines. These latter 
grow more stunted till the limit of aborescent vegetation is reached 
at a height given by Lenk as 4,ocom. (13,123 feet). The slopes of 
the mountain are cultivated to a considerable height, the ranch of 
Coraltitla being situated at an altitude of 3,3r10m. (10,860 feet). 
The smooth, green fields of these ranches, interspersed among the 
forest growth, lend a pleasing variety to the scene. The lower flanks 
of the mountains, except where they are cut into barrancas by 
descending mountain streams, are covered everywhere with soil, so 
that it is only rarely that one finds a rock exposure, or even loose 
bowlders. Wherever these could be found the rock showed remark- 
able uniformity. Everywhere it was the same amphibole-andesite, 
containing porphyritic feldspars 6 to 8mm. in length. In color 
the rock varies from gray to red, according to the state of oxidation 
of the iron. Such a homogeneity of rock over so wide an area is 
remarkable, and favors the view that the mountain originated as a 
fissure eruption rather than as a volcano. It is also remarkable 
that the rock should differ so completely in character from that of 
Popocatepetl. Near the southern end of the mountain Lenk found a 
rock which resembled that of Popocatepetl, in having the hornblende 
replaced by hypersthene. This seems to represent a transition stage, 
but the rock mass of the two mountains differs in a marked degree in 
its constituency. 
Another feature prominently noticed in ascending Ixtaccihuatl was 
the comb-like or aiguille-like character of many of its spurs. These 
usually took the form of ridges extending in a direction at right angles 
to the course of the mountain, and presenting on the western slope 
*A Naturalist in Mexico, p. 110. 
