W.; consequently, the plane of projection, to be. perpendicular to the longitudinal axis of the Cordil lera, should not be placed parallel to the equator, but drawn from the N. E. to the S. W. By reflecting on the particular structure and limits of the group of mountains, in the neighbourhood of the capital of Mexico, we shall find that the reunion of the two sections, No. VII. and VIII. gives a less imperfect representation of the conformation of the country than we should be tempted to believe from purely theoretical ideas. In this mountainous region between the 19° and 20° of latitude, nothing announces a longitudinal crest. There are none of those parallel chains which geologists always admit in their works, and which geographers represent in the most arbitrary manner, in their maps of the two continents, like ranges of elevated dikes. The Cordillera of Anahuac increases towards the north, from whence the inclined planes formed by the eastern and western declivities are not parallel to one another in their middle direction. This direction is almost N. and S. along the coast of the gulf of Mexico, while it is S. E. and N. W. in the declivity opposite the Great Ocean. Hence the sections, to be perpendicular to the lines of declivity, cannot be in the same plane of projection.

VIII. PHYSICAL VIEW OF THE CENTRAL TABLE-LAND OF NEW SPAIN.

The section of the road leading from Mexico to the mines of Guanaxuato, the richest of the known world, was drawn up under my eye at Mexico, by M. Raphael Davalos,* a pupil of the school of mines,

* M. Davalos, as well as M. Juan Jose Rodriguez, a native of the Parral, in the provincias internas, and well informed in

and a very zealous young man. This drawing displays to the naturalist the great elevation of the tableland of Anahuac, which extends to the north much beyond the torrid zone. The extraordinary configuration of the Mexican soil recalls the elevated plains of central Asia. It would be interesting to continue my section from Guanaxuato to Durango and Chihuahua, particularly to Santa Fe in New Mexico. For the table-land of Anahuac, as we shall hereafter prove, preserves towards the north for an extent of more than two hundred leagues more than 2,000,† and for an extent of five hundred leagues more than 800 metres of absolute elevation.

IX, PICTURESQUE VIEW OF THE VOLCANOES OF MEXICO OR LA PUEBLA.

This plate and the immediately following one were destined at first to appear in the physical atlas, which will accompany the historical account of my travels in the equinoxial regions. I mean to unite in that atlas such sketches as will show the physiognomy of the collossal summits which crown the ridge of the Cordilleras, and form as it were their crest. I thought that these contours, compared with those in the excellent itinerary of M. Ebel, or the beautiful drawings of M. Osterwald, might prove interesting to the geologists who wish to study comparatively the Alps

physical science, were so good as to assist me for several months in the construction of a great number of geological maps which will be afterwards published. I am pleased to have an opportunity of giving a public testimony of my gratitude to gentlemen so distinguished for their talents and application.

*Book I. and book III.

† 6,560 feet. Trans.

2,624 feet. Trans.

of Switzerland, and the Andes of Mexico and Peru. Though the object of the work which I now pub. lish is more to describe the territorial riches than the geological constitution of New Spain, I have thought proper to add to the Mexican atlas the picturesque views No 1x. and x. to serve as a supplement to the map of the valley, (plate 111.) and to give a more lively idea of the beauty of the situation of the city of Mexico. These same summits, the Popocatepet! and the Citlaltepetl, the first of which is visible at Mexico and Cholula, and the second at Cholula and Vera Cruz, served me to verify the meridian difference of the city of Mexico and the port of Vera Cruz by a method very advantageous, but hitherto little followed; that of perpendicular bases, azimuths and angles of altitude.*

The city of Mexico is nearer by one half to the two Nevados de la Puebla than the cities of Bern and Milan are to the central chain of the Alps. This great proximity contributes much to give an awful and majestic aspect to the Mexican volcanoes. The contours of their summits, covered with eternal snow, appear so much the more marked, as the air through which the eye receives the rays is more rare and transparent. The snow is of a most extraordinary brilliancy, particularly when it descends from a sky of which the blue is always deeper than that of the sky which we see from our plains of the temperate zone. The observer finds himself, in the city of Mexico, in a stratum of air, whose barometrical pressure is only 585 millimetres. It is easy to conceive, that the extinction of light must be very trifling in an atmosphere so little condensed, and that the summit of the Chimborazo, or the Popocatepetl,

See above, p. xxiii. and my Recueil d'Observations Astronomiques, vol. I. p. 373.

Nearly twenty-three inches. Trans

seen from the plains of Riobamba or Mexico, must exhibit more distinct contours than if they were seen at the same distance from the shores of the ocean. : The Iztaccihuatl and the Popocatepetl, of which the latter has the conical form peculiar to the Cotopaxi and the Pic d'Orizaba, are called indiscriminately in the country the volcanoes of la Puebla or Mexico, because they are equally well distinguished from these two cities. I have no doubt that the Iztaccihuatl, which Cardinal Lorenzana calls Zihualtepec, is an extinguished volcano; but no Indian tradition goes back to the time when this mountain, which in its contours resembles the volcano of Pichincha, vomited forth fire. The same observation applies to the Nevado de Toluca. The Spaniards have been in the habit, from the first times of the conquest, of naming every insulated summit volcan, which enters into the region of perpetual snow. The words nevado and volcan are frequently confounded: I have even heard at Quito, the strange expressions volcan de nieve and volcan de fuego.* The Cotopaxi, for example, is reputed a fire-volcano, because its periodical eruptions are known, while the Corazon and the Chimborazo are called snow-volcanoes, because the natives suppose that the fire is concealed in them. In the kingdom of Guatimala,† and in the Philippine Islands, they call water-volcanoes (volcanes de agua) those which inundate the surrounding country. From these examples, we may see that the word volcan, in Spanish maps, is frequently used in a sense quite different from what is understood by it among the other nations of Europe.

M. Don Luis Martin drew the volcanoes of la Puebla as they appear in a clear day from the Terrace of

Snow-volcano and fire-volcano.

Trans.

† "En Goatemala hay dos volcanos, uno de fuego y otro de agua." (Lorenzana, in a note to the Letters of Cortez.)

the School of Mines; (Seminario Real de Mineria). A justly celebrated artist, who honours me with a parti cular friendship, M. Gmelin of Rome, was obliging enough to retouch the drawing of M. Martin, and my sketch of the Pic d'Orizaba. The contours were nowise altered, and I have no doubt that the hand of a great master will easily be perceived in the distribution of shade, as well as in the effect of the chiaro-scuro.

It may be useful to observe, that the volcanoes of la Puebla were drawn in the month of January, in a season when the inferior limit of perpetual snow almost descended to the height of the summit of the Peak of Teneriffe, or to 3,800 metres of absolute elevation.* During my stay at Mexico, I saw such immense falls of snow in the mountains, that the two volcanoes were almost united by one band of snow. The maximum† of elevation of the region of snow, which I found in the month of November, 1803, was nearly 4,560 metres.‡

The Sierra Nevada, or Iztaccihuatl, is only a few metres higher than Mount Blanc; but the Popocatepetl surpasses Mount Blanc 625 metres in height. Besides, the plain which extends from the city of Mexico to the foot of the volcanoes is itself more elevated than the summit of Mount d'Or, and the famous passages of the lesser St. Bernard, Mount Cenis, Simplon, and the ports of Gavarnie and Cavarere.

It was between these two volcanoes of la Puebla that Cortez passed with his troop and six thousand Tlascaltecs, on his first expedition against the city of