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, and a very zealous young man, This drawing displays to the naturalist the great elevation of the table-land 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 tableland of Anahuac, as we shall hereafter prove †, preserves towards the north for an extent of more

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

than two hundred leagues more than 2000*, and for an extent of five hundred leagues more than 800 metres of absolute elevation.

IX. PICTURESQUE VIEW OF THE VOLCANOS 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 colossal 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 of Switzerland, and the Andes of Mexico and Peru. Though the object of the work which I now publish 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. Ix 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 Popocatepetl and the Citlaltepetl, the first of which is visible at Mexico

* 6560 feet. Trans.

2624 feet. Trans.

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 volcanos. 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 millimetrest. 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, seen from the plains of Riobamba or Mexico, must exhibit

* See above, p. xxiii. and my Recueil d'observations astronomiques, vol. I. p. 373.

Nearly twenty-three inches. Trans.

more distinct contours than if they were seen at the same distance from the shores of the ocean.

The Istaccihuatl and the Popocatepetl, of which the latter has the conical form peculiar to the Cotopaxi and the Peak of Orizaba, are called indistinctly in the country the volcanos 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 expreffions Volcan de Niece 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-volcanos, because the natives suppose that the fire is concealed in them In the kingdom of Guatimala †, and in the Philip

* 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 Cortes.)

pine Islands, they call water-volcanos (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 volcanos of la Puebla as they appear in a clear day from the Terrace of the School of Mines-(Seminario Real de Mineria). A justly celebrated artist, who honours me with a particular 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 volcanos 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 3800 metres of absolute elevation *. During my stay at Mexico, I saw such immense falls of snow in the mountains, that the two volcanos were almost united by one band of snow. The maximum † of elevation of the region of snow, which I found in the

* About 12460 feet. Trans.

+ See book i. chap. ii.