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hundred and twelve mines, and the new division of the country into intendancies: those mines which have been worked are there indicated from a catalogue which the supreme tribunal of mines caused to be drawn upon the spots, through the whole extent of that vast empire. I have distinguished by particular signs the places which are the seats of the Deputaciones de Alinus, and the sites of the mines which depend on them. The catalogue with which I was furnished very often marked the rhomb and the distance from some more considerable town. These notes I combined with what I found in the old manuscript maps, among which those of Velasquez were of the greatest assistance to me. This labour was equally minute and troublesome. When any map did not bear the name of the mine, I placed it simply according to the situation in the catalogue, reducing the itinerary distances or leagues of the country into absolute distances, from combinations furnished by analogous cases. The population of New Spain being concentrated on the great interior plain of the central chain, it follows that the map of Mexico is covered very un. equally with names. It must not however be supposed that there are districts entirely uninhabited, wherever the map indicates neither village nor hamlet. I wished only to enter places whose po. sition was the same in several manuscript maps from which I laboured; for the most part of the American maps, executed in Europe, are filled with
names whose existence is unknown in the country itself. These errors are perpetuated, and it often becomes extremely difficult to conjecture their origin. I chose rather to leave a vacant space in my map than to draw from suspicious sources.
The indication of the chains of mountains presented difficulties which can only be felt by those who have been themselves employed in con- . structing geographical maps. I preferred hatchings (hachures) in orthographical projection, to the method of representing mountains in profile. This last, the oldest and most imperfect of all, occasions a mixture of two sorts of very heterogeneous projections. Yet I will not dissemble that this inconvenience is almost balanced by a real advantage. The old method furnishes signs which announce vaguely " that t'e country is hilly, that there exists mountains in such or such a province.” The more this hieroglyphical language is vague the less it exposes to error. The method of batching, on the contrary, forces the drawer to say more than he knows, more than it is even possible to know of the geological constitution of a vast extent of territory. To look at the last maps of Asia Minor and Persia, one would believe that learned geologists have ascertained the relative height, the limits, and direction of the mountains. We discover there chains which wind and branch out like rivers ; we are tempted to believe that the Alps and Pyrenees are less known than these
distant countries. However, well informed peo. ple who have gone through Persia and Asia Minor assert, that the grouping of the mountains there differs entirely from the forın in which they appear in the large map of Asia, published by Arrowsmith, so often copied both in France and Germany.
The waters rindoubtedly in some sort give the delineation of the country; but the courses of rivers merely indicate the differ nce of level which exists in the extent of territo y through which they run. A knowledge of the great vallies or of the basins; an examination of the points where rivers take their rise, are certainly extremely interesting to a hydrographical engineer; but it is a false application of the principles of hydrography, when geographers attempt to determine the chains of moun. tains in countries of which they suppose they know the course of the rivers. They suppose that two great basins of water can only be separated by great elevations, or that a considerable river can only change its direction when a group of moun. tains opposes its course. They forget that frequently, either on account of the nature of the rocks, or on account of the inclination of the strata, the most elevated levels give rise to no ri. ver, while the sources of the most considerable rivers are distant from the high chains of moun. tains. Hence the attempts which have been hitherto made to construct physical maps from
theoretical ideas have never been very successful. For the true configuration of the earth is so much the more difficult to be discovered, as the pelagick currents, and the greater number of the rivers which have changed the surface of the globe, have totally disappeared. The most perfect acquaintance with those which have existed, and those which actually exist in our days, might instruct us as to the slope of the vallies, but by no means as to the absolute height of the mountains, or the position of their chains.
I have traced on my map of New Spain the direction of the Cordilleras, not from vague sup positions or hypothetical combinations, but from a great variety of data furnished by persons who had visited the Mexican mines. The most ele. vated groupe of mountains is to be found in the environs of the capital, under the 19° of latitude. I examined myself the part of the Cordilleras of Analiuac, between the parallels of 16° 50' and 21° 0', for a breadth of more than 140 leagues. It was in this region that I made the greatest number of barometrical and geo. desical measurements, of which the results served for my geological sections. The manuscript maps of M. Velasquez, and of MM. Costanzo and Pagaza, were of great use to me for the northern provinces. M. Velasquez, director of the Tribunal de Afineria, travelled over the greater part of New Spain; and he traced on the map which we have already cited the branches of the Sierra Madre de Anahuac, the eastern branch which runs from Zimapan towards Charcas and Monterey, in the small kingdom of Leon, and the western branch which extends from Bolaños to the Presidio de Fronteras. The manuscript memoirs of M. Sonnenschmidt, a learned Saxon mineralogist, who visited the mines of Guanaxuato, Zacatecas, Chihuahua and Catorce, and the labours of M. del Rio, professor in the school for mines of Mexico, and of Don Vincente Valencia, residing at Zacatecas, have also furnished me with very useful information. I owe much also to the celebrated D'Elhuyar at Mexico; M. Chovell at Villalpando; M. Abad at Valladolid; M. Anza at Tasco; Colonel Obregon at Catorce; and a great number of rich proprietors of mines and religious missionaries, who were so good as to take an interest in my work. Notwithstanding all the pains I took to be informed as to the direction of the chains of mountains, I am far from regarding this part of my work as perfect. Occupied these twenty years in examining mountains and collecting materials for a geological atlas, I well know how hazardous an undertaking it is to trace the mountains on an extent of territory of 118,000 square leagues. .