2,300 feet in largest diameter. He determined the height to be
19,613 feet above the ocean. Its real elevation above the sea is
somewhat masked, owing to the fact that it rises from the high plain of
Tapia, which is itself 8,900 feet above the sea surface. The smaller
peak on the right (Fig. 2) is that of Carihuairazo, which reaches an
elevation of over 16,000 feet.

Chimborazo, in Columbia, province of Quito, is one of the loftiest of
the chain of the Andes, and is situated in lat. 1 deg. 30' S., long. 78 deg. 58'
W. Though not in a state of activity, it is wholly composed of volcanic
material, and reaches an elevation of over 20,000 feet above the ocean;
its sides being covered by a sheet of permanent snow to a level of 2,600
feet below the summit.[6] Seen from the shores of the Pacific, after the
long rains of winter, it presents a magnificent spectacle, "when the
transparency of the air is increased, and its enormous circular summit
is seen projected upon the deep azure blue of the equatorial sky. The
great rarity of the air through which the tops of the Andes are seen
adds much to the splendour of the snow, and aids the magical effect of
its reflection."

Chimborazo was ascended by Humboldt and Bonpland in 1802 almost to the
summit; but at a height of 19,300 feet by barometrical measurement,
their further ascent was arrested by a wide chasm. Boussingault, in
company with Colonel Hall, accomplished the ascent as far as the foot of
the mass of columnar "trachyte," the upper surface of which, covered by
a dome of snow, forms the summit of the mountain. The whole mass of the
mountain consists of volcanic rock, varieties of andesite; there is no
trace of a crater, nor of any fragmental materials, such as are usually
ejected from a volcanic vent of eruption.[7]

_Lava Crater-Cones._--A third form of volcanic mountain is that which
has been built up by successive eruptions of basic lava, such as basalt
or dolerite, when in a molten condition. These are very rare, and the
slope of the sides depends on the amount of original viscosity. Where
the lava is highly fused its slope will be slight, but if in a viscous
condition, successive outpourings from the orifice, unable to reach the
base of the mountain, will tend to form a cone with increasing slope
upwards. Mauna Loa and Kilauea, in the Hawaiian Group, according to
Professor J. D. Dana, are basalt volcanoes in a normal state. They have
distinct craters, and the material