Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/229

Rh MEXICO 215 Horn to Behring s Strait. But more recent research, and especially the surveys made by the French staff during the military operations between 186 1-67, l have shown that this grand generalization must be abandoned. In remote geological epochs a marine channel seems to have flowed between the northern and southern sections of the New World at the isthmus of Panama, while Mexico itself appears to be mainly a distinct geographical region of relatively recent upheaval. Here there nowhere exists a continuous mountain range, to which might properly be applied the designation &quot; Cordillera of the Andes,&quot; an expression which in any case is not current north of the isthmus of Tehuantepec. Mexico forms, on the contrary, a vast table-land, somewhat in the shape of a cornucopia, with its narrow end tapering to the south-south-east, its convex and concave sides facing the Pacific and Atlantic respectively, and with a general inclination northwards. Most of the so-called Cordilleras are merely the &quot; cumbres &quot; or escarpments of this plateau, which falls abruptly towards the Atlantic, and through a series of well-marked terraces (formerly lacustrine basins) towards the Pacific. Thus the carriage road from the capital runs in tolerably easy stages successively through the Tetla (8000 feet), Mescala (5500), Papagallo (1800), and Peregrine (1600) valleys down to Tepes within 40 miles of the seaport of San Bias. But the southern central plateau of Anahuac maintains its mean elevation of 7000 to 8000 feet almost everywhere to within 35 or 40 miles of the Atlantic. Hence the railway opened in 1872 between Vera Cruz and the capital has had to be carried by tremendously steep gradients to a height of nearly 8000 feet within a total distance of 263 miles. 2 The general but gradual northerly tilt of the table-land is shown by the altitudes of the capital, Durango, Chihuahua, and Paso del Norte on the United States frontier, which are respectively 7600, 6630, 4600, and 3800 feet. At the same time the scarps rise in many places con siderably above the mean level of the plateau, which is itself intersected and broken into a number of secondary valleys by several short cross ridges, generally following the normal direction from north-north-west to south-south east. The most continuous range is the Sierra Madre of the Pacific, which may be traced at a mean elevation of over 10,000 feet from Oajaca to Arizona, and which from Guadalajara to the northern frontier is crossed by no carriage route. Parallel to this is the Lower Californian range (Sierra de la Giganta, 3000 feet), which, however, falls abruptly eastwards, like the Atlantic escarpments. The Californian peninsula seems to have been detached from the mainland when the general upheaval took place which produced the vast chasm now flooded by the Gulf of California. Corresponding with the Sierra Madre of the Pacific on the west are the more interrupted eastern scarps of the central plateau, which sweep round the Gulf of Mexico as the Sierras Madres of Nuevo-Leon and Tamaulipas at an elevation of about 6000 feet. These are crossed by the carriage routes from Tula to Tampico (highest pass 4820 feet), from Saltillo to Monterey (3400), and at several other points. Of the central cross ridges the most important orogra- phically and historically is the Cordillera de Anahuac, 3 1 The results of these surveys are embodied in the Carte du Mexique, scale 1 : 3,000,000, published at Paris in 1873. - In the steepest parts the mean is 2 51 in 100, or 133J feet to the mile. The exact elevation of the capital above the sea at Vera Cruz appears to be 7550 feet, or 80 more than Humboldt s estimate. 3 The term Anahuac, meaning in Aztec &quot; near the water,&quot; seems to have been originally restricted to the central lacustrine basin of Tenochtitlan. But when the Aztecs reached both oceans they extended it to the Pacific coast between Tututepec and Guatemala (Anahuac- Ayotlan), and to the Atlantic coast between the Alvarado and Tabasco rivers (Auahuac-Xicalanco). The original use of the word is which surrounds the Mexican (Tenochtitlan) and Puebla valleys, and which is supposed to culminate with Popo catepetl (17,853 feet) and Ixtaccihuatl (15,705). 4 But these giants belong to a different or rather a more recent system of igneous upheaval, running from sea to sea between 18 59 and 19 12 N. in almost a straight line east and west, consequently nearly at right angles to the main axis of the central plateau. The line is clearly marked by several extinct cones and by five active or quiescent volcanoes, of which the highest is Popocatepetl, lying south of the capital nearly midway between the Pacific and Atlantic. East of this central point of the system are Citlaltepetl, better known as the Peak of Orizaba (17,176 feet), 70 miles inland, and San Martin or Tuxtla (9708 feet) on the coast south of Vera Cruz, to which correspond on the west the recently upheaved Jorullo (4000 feet) in Michoacan, Colima (12,800) near the coast in Jalisco, and the volcanic Revillagigedo group in the Pacific. South of this line, and nearly parallel, are the Sierras of Guerrero, and south of the Tehuantepec isthmus those of Oajaca and Soconusco towards the Guatemala frontier. In the same direction run the islands of Cuba and Hayti, which probably belong to the same Central- American system. Mexico is thus physically connected through its older plateau formations with the North-American table-lands, and through its more recent volcanic upheavals with the Central-American igneous region. But as it advances northwards this region loses in underground energy ; hence, notwithstanding the remarkable upheaval of Jorullo in 1759, the Mexican cones show little signs of activity, 5 and the land is now scarcely ever wasted by violent earth quakes. Such phenomena are most frequent in the Puebla valley ; but, although often accompanied by the peculiar underground rumblings known as bramidos, they are seldom of a destructive character. The natives speak of them rather as temblores, or &quot; tremblings,&quot; than true terremotos. 6 In a region where lofty ranges and plateau forma- Hydro- tions with steep escarpments approach almost everywhere g ra P llv - to within a few miles of the coast, little space is left for the development of large river basins. Most of the streams are little more than mountain torrents rushing impetuously from terrace to terrace seawards. Many also still current amongst the natives as practically synonymous with Central Mexico. As a strictly geographical expression it is vaguely and often incorrectly used by modern writers. 4 This elevation is based on the calculations of Humboldt, Glennie, and Gerolt ; but in 1857 Sonntag assigned an extreme height of over 17,000 feet to the highest peak of Ixtaccihuatl. Popocatepetl is usually supposed to be the highest point of North America ; but the recent United States surveys have transferred this honour to Mount Elias on the Alaska coast, which appears to be certainly over 19,000 feet high. 5 Popocatepetl emits smoke, whence its name, meaning in Aztec &quot;Smoking Mountain,&quot; from popoca &quot;to smoke,&quot; and tepetl &quot; moun tain.&quot; Since the conquest three eruptions have been reported (1519, 1539, 1540) ; but the geological evidence seems to indicate that there has been no volcanic action for thousands of years. Orizaba, whose native name means &quot;Star Mountain,&quot; has been quiescent since 1566. Colima still frequently ejects ashes and smoke; but both Jorullo and Tuxtla are quiescent, the last having been silent since the violent eruption of March 2, 1793. Even the Mai-pays, or hot dis trict round Jorullo, has cooled down, and is now again clothed with vegetation. It is noteworthy that the seismic waves flow normally along the indicated line from east to west, thereby confirming Humboldt s view that under about 19 N. there is a deep rent in the earth s crust, through which at different periods the underground fires have broken at various points between the Gulf of Mexico and the Revilla gigedo group. &quot;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&quot; (Egloffstein, p. 37).