238 
of results useful to the progress of science ; the 
traveller finds himself on ground covered with 
snow, in a stratum of air, the chemical mixture 
of which is the same as that of the lower re- 
gions, and in a situation in which delicate expe- 
riments cannot be made with all the exactness 
requisite. 
If we compare the fifth, tenth, and sixteenth 
plates of this work with those of the geographi- 
cal and physical Atlas, which acccompanies my 
Essay on the Kingdom of New Spain, we dis- 
tinguish three kinds of principal forms belonging 
to the high tops of the Andes. The volcanoes 
which are yet burning, those which have but a 
single crater of extraordinary size, are conic 
mountains, with summits truncated in a greater 
or less degree : such is the figure of Cotopaxi, of 
Popocatepec, and the Peak of Orizaba. Volca- 
noes, the summits of which have sunk after a long 
series of eruptions, exhibit ridges bristled with 
points, needles leaning in different directions, 
and broken rocks falling into ruins. Such is the 
form of the Altar, or Capac-Urcu, a mountain 
once more lofty than Chimborazo, and the de- 
struction of which is considered as a memorable 
period in the natural history of the New Conti- 
nent ; such] is the form also of Carguairazo, a 
great part of which fell in on the night of the 
19th of July, 1698. Torrents of water and mud 
then issued from the opened sides of the moun- 
