hed; that of the Pacific; and the hydrographic
entities of the great plateau. In the first of these is the vast region
of the northern part of Mexico, which, with Texas and New Mexico,
drains into the Rio Grande and thence into the Gulf; the long littoral
of the Gulf Coast, whose _divortia aquarum_, or water-parting, is
formed by the Eastern Sierra Madre; and the peninsula of Yucatan. In
the second is the vast stretch of the Pacific slope, whose _divortia
aquarum_ is the Western Sierra Madre; the peninsula of Lower
California, and the southern side of the region south of the Isthmus of
Tehuantepec. In the third are the intra-montane portions of the great
plateau, whose waters have no outlet or natural source of exhaustion
except that by evaporation, such as the great plains known as the
Bolson of Mapimi; and the Valley of Mexico. Topographically,
however--apart from the three climatic zones of hot, temperate, and
cold lands--the country is divided orographically into two portions by
the Isthmus of Tehuantepec, the former consisting of the characteristic
mountain-chains and great plateau, and the latter of the immense plains
of Yucatan, with a low elevation of not more than 300 feet above
sea-level.

The formation of Mexico has not given rise to the existence of great or
navigable rivers nor, indeed, of harbours. With few exceptions rivers
are torrential in character, although some are of considerable length.
The Rio Grande, which forms the northern boundary of the United States,
and is therefore international in character, is 1,500 miles in length;
rising in Colorado and passing through New Mexico in the United States,
and thence entering between Texas and Chihuahua, it is joined by two
large tributaries--the Pecos on the American and the Conchos river on
the Mexican side. Thence it flows south-eastwardly to the Gulf of
Mexico. The waters which enter Mexican territory are scarce, as they
have been taken out for irrigation purposes in American territory. The
Lerma, or Santiago, river is the next in point of length, and is a
stream of considerable importance, dividing the main portion of Mexico
topographically into two subdivisions. It flows for 540 miles from its
source in the mountains near Toluca, passing through the beautiful Lake
Chapala--the largest in Mexico--and forms the great cascade of
Juanacatlan, the Niagara of Mexico; traverses the State of Jalisco,
where it is joined by numerous affluents, and discharges in