these are enumerated in the chapter corresponding to the natural
products. Among the 115 or more species of timber and wood for
constructional purposes are oak, pine, mahogany, cedar, and others,
whilst the list of fibrous and medicinal plants, gum-bearing trees, as
india-rubber, _chicle_, &c., tinctorial and resinous trees, edible
plants and fruits, is of much interest and value. In the tropical
lowlands the country is so thickly wooded as in places to be
impassable, except by clearing trails and felling trees. There are
virgin forests of great extent in these sparsely populated regions,
both of the Pacific and Atlantic slopes. Upon the great plateau,
however, and the mountain slopes immediately adjoining it conditions
are very different. Great tracts of country are, as elsewhere
described, absolutely bare of vegetation, both naturally and by reason
of the inroads made upon the forests by civilised man. The great desert
tracts never had tree or plant life in profusion, but the hilly regions
bounding these, and the inward slopes of the Sierra Madres were
formerly covered with thick forests, and in some regions are still so
covered. But they have been denuded in certain regions of their timber,
principally for fuel, as native coal has been unknown until recently,
and is difficult of transport. This denudation has had an undoubted
effect upon the rainfall, and has served to change the climatic
conditions in these regions. In other upland regions, however, the
splendid and extensive forests of oak and pine form marked features of
the landscape, and are of much industrial value.

[Illustration: VEGETATION IN THE TROPICAL FORESTS.]

The diversity of climatic and botanical conditions of Mexico gives as a
natural corollary a variety of animal life, and the _fauna_ is an
extensive one, including, with small exception, all the species of
North America on the one hand, and of South America on the other. Those
of the former, naturally, are found upon the great plateau; those of
the latter in the tropical lowlands. Among the main exceptions are the
llama and alpaca, the domestic wool-bearing animals of the camel
family, and kindred varieties, which do not exist in Mexico, nor are
found anywhere in the world outside the highlands of Peru and Bolivia.
Indeed, native Mexico, before the introduction of the equine race from
Europe, had no beast of burden whatever, such as the llama afforded to
the South American aboriginal peoples.