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Tenochtitlan to the Rio de Panuco, and by which, forgetting that Mexico is 9277 metres* elevated above the level of the sea, a navigation has been projected between the capital and the western coast; 3. The Rio de Zacatula ; 4. The great river of Santiago, formed by the junction of the rivers Lerma and las Laxas, which might carry the flour of Salamanca, Zelaya, and perhaps the whole intendancy of Guadalaxara, to the port of San Blas, or the coast of the Pacific Ocean.
The lakes with which Mexico abounds, and of which the most part appear annually on the decline, are merely the remains of immense basins of water, which appear to have formerly existed on the high and extensive plains of the Cordillera. I siall merely mention in this physical view the great lake of Chapala in New Gallicia, of nearly 160 square leagues, double the size of the lake of Constance; the lakes of the valley of Mexico, which include a fourth part of its surface; the lake of Patzcuaro, in the intendancy of Valladolid, one of the most picturesque situations wbich I know in either continent; and the lakes of Mexiitlan and Parras in New Biscay.
The interior of New Spain, especially a great part of the high table-land of Anahuac, is destitute of vegetation ; its arid aspect brings to mind in some places the plains of the two Castilles. Se
. * 7468 feet. Trans,
veral causes concur to produce this extraordinary effect. The evaporation which takes place on great plains is sensibly increased by the great elevation of the Mexican Cordillera. On the other hand, the country is not of sufficient elevation for a great number of summits to penetrate the region of perpetual snow. This region commences under the equator at 4800 metres * (2460 toises), and under the 45° of latitude at 2550 + metres (1300 toises) above the level of the sea. In Mexico the eternal snows commence, according to my measurements in the 199 and 20° of latitude, at 46001 metres (23.50 toises) of elevation. Hence, of six colossal mountains which nature has ranged in the same line, between the parallels of 19'and 197, only four, the Pic d'Orizaba, Popocatepetl, Iztaccihuatl, and the Nevado de Toluca, are covered with perpetual snow, while the two others, the Cofre de Perote, and the Volcan de Colima, remain uncovered the greatest part of the year. To the north and south of this parallel of great elevations, beyond this singular zone, in which the new Volcan de Jorullo is also ranged, there are no mountains which exhibit the phenomenon of perpetual snow.
These snows, at the period of their minimum, in the month of September, never descend in the
* 15747 feet. Trans.
$ 15091 feet.
+ 8365 feet. Trans,
parallel of Mexico below 4500 metres*. But in the month of January they fall as low as 3700 metrest: this is the period of their maximum.
The oscillation of the limits of perpetual snow is, consequently, under the latitude of 19°, from one, season to the other 800 metres I; while under the equator it never exceeds 60 or 70 metres S. We must not confound these eternal snows with the snows which in winter accidentally fall in much. lower regions. Even this phenomenon, like every other in nature, is subject to immutable laws worthy of the investigation of philosophers. This ephemeral snow is never observed under the equator below 3800 or 3900 metres ll; but in Mexico, under the latitude of 18° and 22° it is commonly seen at an elevation of 3000 metres . Snow has even been seen in the streets of the capital of Mexico at 2277** metres, and 400 metres ft lower in the city of Valladolid.
In general, in the equinoxial regions of New Spain, the soil, climate, physiognomy of vegetables, all assume the character of the temperate zones. The proximity of Canada, the great breadth of the new continent towards the north, the mass of
* 14763 feet. Trans. : + 12138 feet. Trans.
2624 feet. Trans. $ 196 or 229 feet. Trans,
snows with which it is covered, occasion in the Mexican atmosphere frigorifications by no means to be expected in these regions.
If the table-land of New Spain is singularly cold in winter, its temperature is, on the other hand, much higher in summer than what was found by the thermometrical observations of Bouguer and La Condamine in the Andes of Peru. The great mass of the Cordillera of Mexico, and the immense extent of its plains, produce a reverberation of the solar rays, never observed in mountainous countries of greater inequality. This heat, and other local causes, produce the aridity of these fine regions.
To the north of 20', from the 22° to the 30° of latitude, the rains which only fall in the months of June, July, August, and September, are very unfrequent in the interior of the country. We have already observed that the great height of this tableland, and the small barometrical pressure of the rarefied air, accelerate the evaporation. The ascending current or column of warm air which sises from the plains prevents the clouds from precipitating in rain to water a land, dry, saline, and destitute of vegetation. The springs are rare in mountains composed principally of porous amygdaloid, and fendilated (fendillé) porphyry. The filtrated water, in place of collecting in small subterraneous basins, is lost in the crevices which old volcanic revolutions have opened, and only is
sues forth at the bottom of the Cordillera. It forms a great number of rivers on the coast, of which the course is very short on account of the configuration of the country.
The aridity of the central plain, the want of trees, occasioned, perhaps, in a good measure by the length of time the great vallies have remained covered with water, obstruct very much the working of the mines. These disadvantages have augmented since the arrival of Europeans in Mexico, who have not only destroyed without planting, but in draining great extents of ground have occasioned another more important evil. Muriate of soda and lime, nitrate of potash, and other saline substances, cover the surface of the soil, and spread with a rapidity very difficult to be explained.
Through this abundance of salt, and these efflorescences, hostile to cultivation, the table-land of Mexico bears a great resemblance in many places to T'hibet and the saline steppes of central Asia. In the valley of Tenochtitlan, particularly, the sterility and want of vigorous vegetation have been sensibly augmenting since the Spanish conquest; for this valley was adorned with beautiful verdure when the lake occupied more ground, and the clayey soil was washed by more frequent inundations.
Happily, however, this aridity of soil, of which we have been indicating the principal physical causes, is only to be found in the most elevated