Cerro de Sincoque), constituting a fourth part of it, has been cut to an extraordinary depth. At the point where the ridge is highest near the old well of Don Juan Garcia, for more than a length of 800 metres*, the cut in the mountains is from 45 to 60 metres † in perpendicular depth. From the one side to the other, the breadth at top is from 85 to 110 metres §. The depth of the cut is from 30 to 50 metres, for a length of more than 3500 metres ¶. The water-course is generally only from three to four metres** in breadth; but in a great part of the desague the breadth of the cut is by no means in proportion to its depth, so that the sides in place of having a slope of 40° or 50° are much too rapid, and are perpetually falling in. It is in the Obra del Consulado where we principally see the enormous accumulations of moveable earth which nature has deposited on the porphyries of the valley of Mexico. I have reckoned, in descending the stair of the viceroys, 25 strata of hardened clay, with as many alternate strata of marle, contain

* 2624 feet. Trans. † From 147 to 196 feet. Trans. From 278 to 360 feet. Trans.

§ To have a clearer idea of the enormous breadth of this trench in the Obra del Consulado, we have only to recollect that the breadth of the Seine at Paris is at Pont Bonaparte 102 metres (334 English feet), at Pont-Royal 136 metres (446 feet), and at the Pont d'Austerlitz, near the botanical garden, 175 metres (574 feet).

From 98 to 131 feet. Trans. T11,482 feet. Trans. ** From 9.84 to 13.1 feet. Trans.

ing fibrous calcareous balls of a cellular surface. It was in digging the trench of the desague that the fossile elephant bones were discovered, of which I have spoken in another work *.

On both sides of the cut we see considerable hills formed of the rubbish, which are gradually beginning to be covered with vegetation. The extraction of the rubbish having been an infinitely laborious and tedious operation, the method of Enrico Martinez was at last resorted to. They raised the level of the water by small sluices, so that the force of the current carried along the rubbish thrown into the water-course. During this operation, from 20 to 30 Indians have sometimes perished at a time. Cords were fastened round them, by which they were kept suspended in the current for the sake of collecting the rubbish into the middle of it; and it frequently happened that the impetuosity of the stream dashed them against detached masses of rock, which crushed them to death.

We have already observed that from the year 1643, the branch of Martinez's canal, directed towards the lake of Zumpango, had filled up, and that by that means (to use the expression of the Mexican engineers of the present day) the desague had become simply negative; that is to say, it prevented the river of Guautitlan to dis

* In the Recueil de mes Observations de Zoologie et d'Anatomie comparée.

charge itself into the lake. At the period of the great rises the disadvantages resulting from this state of things were sensibly felt in the city of Mexico. The Rio de Guautitlan, in overflowing, poured part of its water into the basin of Zumpango, which, swelled by the additional confluents of San Mateo and Pachuca, formed a junction with the lake of San Christobal. It would have been very expensive to enlarge the bed of the Rio de Guautitlan, to cut its sinuosities, and rectify its course; and even this remedy would not have wholly removed the danger of inundation. The very wise resolution was therefore adopted at the end of the last century, under the direction of Don Cosme de Mier y Trespalacios, superintendant general of the desague, of opening two canals to conduct the water from the lakes of Zumpango and San Christobal to the cut in the mountain at Nochistongo. The first of these canals was begun in 1796, and the second in 1798. The one is 8900, and the other 13,000 metres in length. The canal of San Christobal joins that of Zumpango to the south-east of Huehuetoca, at 5000 metres† distance from its entry into the desague of Martinez. These two works cost more than a million of livres. They are water-courses, in which the

* 29,228 and 42,650 feet. Trans. † 16,404 feet. Trans. $ 41,670. sterling. Trans.

level of the water is from 8 to 12 metres* lower than the neighbouring ground; and they have the same defects on a small scale with the great trench of Nochistongo. Their slopes are much too rapid; in several places they are almost perpendicular. Hence the loose earth falls so frequently in, that it requires from 16,000 to 20,000 francs annually to keep these two canals of M. Mier in a proper condition When the viceroys go to inspect (hacer la visita) the desague (a two days' journey, which formerly brought them in a present of 3000 double piastres) they embarked near their palace§ from the south bank of the lake of San Christobal, and went even farther than Huehuetoca by water, a distance of seven common leagues.

It appears from a manuscript memoir of Don Ignacio Castera, present inspector (maestro mayor) of hydraulical operations in the valley of Mexico, that the desague cost, including the repairs of the dikes (albaradones), between 1607 and 1789, the sum of 5,547,670 double piastres. If we add to this enormous sum from

*From 26 to 39 feet. Trans.

+ From 6661. to 8331. sterling. Trans.

6561. sterling. Trans.

§ This pretended Palacio de los Vireyes, from which there is a magnificent view of the lake of Tezcuco, and the volcano of Popocatepec, covered with eternal snow, bears more resemblance to a great farm-house than to a palace.

6 to 700,000 piastres expended in the fifteen following years, we shall find that the whole of these operations (the cut through the mountains of Nochistongo, the dikes, and the two canals from the upper lakes) have not cost less than 31 millions of livres *. The estimate of the expense of the canal du Midi, of which the length is 238,648 metres†, (notwithstanding the construction of 62 locks, and the magnificent reservoir of St. Ferreol) was only 4,897,000 francs; but it has cost from 1686 to 1791 the sum of 22,999,000 of francs to keep this canal in order.

Resuming what we have been stating relative to the hydraulical operations carried on in the plains of Mexico, we see that the safety of the capital actually depends: 1. on the stone dikes which prevent the water of the lake of Zumpango from flowing over into the lake of San Christobal, and San Christobal from flowing into the lake of Tezcuco; 2. on the dikes and sluices of Tlahuac and Mexicaltzingo, which prevent the lakes of Chalco and Xochimilco from overflowing; 3. on the desague of Enrico Martinez, by which the Rio de Guautitlan makes its way through the mountains into the valley of Tula ;

* 1,291,770l. sterling. Trans. + 782,966 feet. Trans. 204,0571. sterling. Trans. 958,3681. sterling. Trans. Andreossy, Histoire du Canal du Midi, p. 289.