764 The Amerwan Naturalist. [August, 
sheets, whose nature was now for the first time made known to the 
Mexicans, the dangerous ascent was accomplished. Huge crevasses 
at short intervals barred the progress of the march, but the point, esti- 
mated to be about 75 yards below the summit, was reached about 10.30 
o’clock in the morning. Two impassable crevasses, cutting the crest 
of the mountain at right angles, prevented a nearer approach to the 
apex. 
Professor Heilprin’s measurements determined the height of this 
mountain to be 16,962 feet, or from 800 to 1,300 feet above that which 
is accorded to it by Mexican geographers. This determination, on 
the other hand, accords very closely (within 11 feet) with the very 
careful, but now generally overlooked, trigonometrical measurements 
made in 1857 by Sonntag, under the auspices of Baron von Miiller. 
It is difficult to account for the low value of the height of this 
mountain given by Humboldt and the Mexican geographers, in view 
of its close proximity to Popocatepetl. So nearly do they appear of 
equal height that the eye at first fails to distinguish which of the two 
summits is the highest. German geographers, however, in a few cases, 
have adopted Sonntag’s measurements, neglecting, however, as in the 
cases of Popocatepetl, to make allowances for the error, in this case 
of 125 feet, which is indicated by the leveling of the Mexican Railway. 
The temperature on the summit of Ixtaccihuatl was found to be 
much lower than on either of the other peaks, being 32 degrees 
Fahrenheit. 
ASCENT OF NEVADA DE ToLuca.—The fourth highest summit of 
the Republic, the Nevado de Toluca, was ascended by Professor 
Heilprin and Mr. Baker on the 25th of April. This mountain, owing 
to its lesser elevation, has a much easier ascent than the others. In 
fact, it can be ascended by horseback to within about 6oo feet of the 
apex. The rim of the broken crater is extremely ragged and narrow, 
descending with almost equal abruptness to the inner and outer faces 
of the volcano. At some points the crest is so attenuated that it can 
be readily straddled. This feature recalls the famous Polnischer 
Kamm of the Carpathian Mountains, which Professor Heilprin 
ascended in 1878, and from which there is obtained a precipitous* 
descent on the one side into Gallicia, and on the other into Hungary. 
The barometric determination of the Nevada de Toluca gave a 
height of 14,952 feet, and gave approximately the mean between the 
determination of Humboldt and those of a class of students from the 
School of Engineers of the city of Toluca. 
