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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 cutits 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 canal's 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 metrest 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. $ 41,6701. 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 piastrest) 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

de

* From 26 to 39 feet. Trans.
† From 6661. to 833l. sterling. Trans.
I 656l. 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 metrest, (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 11.

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 ;

* 1,291,7701. sterling. Trans. + 782,966 feet. Trans. $ 204,0571. sterling. Trans. $958,3681. sterling. Trans. 1 Andreossy, Histoire du Canal du Midi, p. 289.

and, 4. on the two canals of M. Mier, by which the two lakes of Zumpango and San Christobal may be thrown dry at pleasure. :

However, all these multiplied means do not secure the capital against inundations proceed. ing from the north and north-west. Notwithstanding all the expense which has been laid out, the city will continue exposed to very great risks till a canal shall be immediately opened from the lake of Tezcuco. The waters of this, lake may rise, without those of San Christobal bursting the dike which confines them. The great inundation of Mexico under the reign of Ahuitzotl was solely occasioned by frequent rains *, and the overflowing of the most southern lakes, Chalco and Xochimilco. The water rose to five or six metres f above the level of the streets. In 1763, and the beginning of 1764, the capital was from a similar cause in the greatest danger. Inundated in every quarter it formed an island for several months, without a single drop from the Rio de Guautitlan entering the

The Indian historians relate, that at this period great masses of water were seen to fall on the declivities of the mountains in the interior of the country, which contained fishes never found but in the rivers of the warm regions (pescados de tierra caliente); a physical phenomenon difficult of explanation, on account of the elevation of the Mexican table-land.

t 16 and 19 feet. Trans.

Jake of Tezcuco. This overflow was merely occasioned by small confluents from the east, west, and south. Water was every where seen to spring up, undoubtedly from the hydrostatical pression which it experienced in filtration in the surrounding mountains. On the 6th of September, 1772, there fell* so sudden and abundant a shower in the valley of Mexico, that it had all the appearance of a water spout (manga de agua). Fortunately, however, this phenomenon took place only in the north and north-west part of the valley: The canal of Huehuetoca was then productive of the most beneficial effects, though a great portion of ground between San Christobal, Ecatepec, San Mateo, Santa Ines, and Guautitlan, were inundated to such a degree that many edifices became entire ruins. If this deluge had burst above the basin of the lake of Tezcuco, the capital would have been exposed to the most imminent danger. These circumstances, and several others which we have already adverted to, sufficiently prove how indispensable a duty it becomes for the government to take in hand the draining the lakes which are nearest to the city of Mexico. This necessity is daily increasing, because the bottoms of the basins of Tezcuco and Chalco are continually becoming more elevated from the depositions which they receive.

* Informe de Velasquez (manuscript), folio 25.

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