Jorullo (4262 ft.) is said to date from 1759, when its cone was formed,
and Ceboruco (7100 ft.) in the territory of Tepic, shows occasional
signs of activity. Near the coast in the state of Vera Cruz is San
Martin, or Tuxtla (9708 ft.), which has been quiescent since its
violent eruption of the 2nd of March 1793. Orizaba is sometimes
included among the semi-active volcanoes, but this is a mistake.
It has been quiescent since 1566, and is now completely extinct.
Earthquakes are common throughout the greater part of the republic,
especially on the western coast. They are most violent from San
Blas southward to the Guatemala frontier, and some of the Spanish
towns on or near this coast have suffered severely. Chilpancingo,
in Guerrero, was badly shattered in 1902, and in 1907, and in 1909
was reduced to a mass of ruins. The earthquake shocks of the
30th and, 31st of July 1909 were unusually severe throughout
southern Mexico, reducing Acapulco and Chilpancingo to ruins
and shaking the city of Mexico severely. In Acapulco a tidal wave
followed the shock. Slight shocks, or temblores, are of almost daily
occurrence. According to Humboldt’s theory there is a deep rent
in the earth’s crust about the 19th parallel through which at different
periods the underground fires have broken at various points between
the Gulf of Mexico and the Revillagigedo Islands. “Only on the
supposition that these volcanoes, which are on the surface connected
by a skeleton of volcanic rocks, are also united under the surface by
a chain of volcanic elements in continual activity, may We account
for the earthquakes which in the direction mentioned cause the
American continent, from the Gulf of Mexico to the Pacific Ocean,
to oscillate at the same time” (Egloffstein, p. 57).
The lowland or tierra caliente region, which lies between the sierras and coast on both sides of Mexico, consists of a sandy zone of varying width along the shore-line, which is practically a tidewater plain broken by inland channels and lagoons, and a higher belt of land rising to an elevation of about 3000 ft. and formed in great part by the débris of the neighbouring mountain slopes. On the Pacific side there are places where the mountain spurs extend down to the coast, but in general this lowland region ranges from 30 to 40 m. in width, except in southern Vera Cruz, Tabasco, Campeche and Yucatán, where it extends farther into the interior. The talus zone of this region, especially at elevations of 1000 to 3000 ft., is noted for its great fertility and the luxuriance of its vegetation.
There are no large islands on the coast of Mexico, and most of the smaller ones are unimportant. Many of those that fringe the Gulf coast are sand-keys, or parts of a new coast formation. They are commonly barren and uninhabitable. The Isla del Cármen, which partly shuts in the Laguna de Términos (Campeche), is one of the largest of this class, and has the town and port of Cármen at its western extremity. On the northern coast of Yucatán is the small, inhabited island of Holbox or Holboy, and on the eastern coast the islands of Mujeres, Cancum and Cozumel, of which the first and last have a considerable population and good ports. On the Pacific coast there are a number of islands off the rocky shores of Lower California and in the Gulf of California—most of them barren and uninhabitable like the adjacent coast. The largest of these, some of them inhabited, are: Guadalupe—about 75 m. west of the coast on the 29th parallel, which is fertile and stocked with cattle; Cerros, off Viscaino Bay, and Santa Margarita, which partly shelters Magdalena Bay, on the Pacific side; and Angel de la Guarda, Tiburon, San Marcos, Cármen, Monserrate, Santa Catalina, Santa Cruz, San José, Espiritu Santo and Cerralvo in the Gulf. Lying off San Blas in the broad entrance to the Gulf are the Tres Marias, and directly west of Colima, to which it belongs, is the scattered volcanic group of Revillagigedo.
The peculiar surface formation of Mexico—a high plateau shut in by mountain barriers, and a narrow lowland region between it and the coast—does not permit the development of large river basins. Add to this the light rainfall on the plateau and a lack of forests, and We have conditions which make large rivers impossible. The hydrography of Mexico, therefore, is of the simplest description—a number of small streams flowing from the plateau or mountain slopes eastward to the Gulf of Mexico and westward to the Pacific. Most of these are little more than mountain torrents, but one has a course exceeding 500 m., and few have navigable channels. The principal watershed is formed by the sierras of the state of Mexico, from which streams flow north-east to the Gulf of Mexico, north-west to the Pacific and south-west to the same coast below its great eastward curve. The Rio Grande del Norte, or Rio Bravo, on the northern frontier, is practically an American river, as it rises in American territory and receives very little water from the Mexican side. Its larger Mexican tributaries are the Rio de los Conchos, Salado and Pesqueria. Of the Suchiate and Hondo, which form part of Mexico’s southern boundary, the first is a short, impetuous mountain torrent flowing into the Pacific, and the other a sluggish lowland stream rising in north-eastern Guatemala and flowing north-east through a heavily forested region to Chetumal Bay. The peninsula of Yucatán has no rivers, and that of Lower California only a few insignificant streams in the north. This is due to the porosity of the soil in the former, and the very limited rainfall in the latter. The largest rivers of Mexico are: the Rio Grande de Santiago, called the Lerma above Lake Chapala, rising in the state of Mexico and flowing westward across Guanajuato, Jalisco and
