[footnote] *See my table of the height of the line of perpetual snow, in
both hemispheres, from 71 degrees 15' north lat. to 53 degrees 54' south
lat., in my 'Asie Centrale', t. iii., p. 360.
The snow-line which, under the equator in South America, attains an
elevation equal to that of the summit of Mont Blanc in the Alps, and
descends, according to recent measurements, about 1023 feet lower toward the
northern tropic in the elevated plateaux of Mexico (in 19 degrees north
latitude), rises, according to Pentland, in the southern tropical zone (14
degrees 30' to 18 degrees south latitude), being more than 2665 feet higher
in the maritime and western branch of the Cordilleras of Chili than under
the equator near Quito on Chimborazo, Cotopaxi, and Antisana. Dr. Gilles
even asserts that much further to the south, on the declivity of the volcano
of Peuquenes (latitude 33 degrees), he found the snow-line at an elevation
of between 14,520 and 15,030 feet. The evaporation of the snow in the
extremely dry air of the summer, and under a cloudless sky, is so powerful,
that the volcano of Aconcagua, northeast of Valparaiso (latitude 32 degrees
30'), which was found in the expedition of the Beagle to be more than 1400
feet higher than Chimborazo, was on one occasion seen free from snow.
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