in the vicinity of which the water accumulates until it hollows out a basin, or reservoir, by undermining the banks on each side, the consequences will, in a few years, become very serious, and may probably render the whole work useless, at the moment when its services are most indispensable.
If in an effective state, the canal of Nŏchistōngŏ is regarded as fully sufficient to ensure the Capital against any risk of inundation from the North; but to the South, as Humboldt very justly observes, no precautions have been taken; not because there is no danger of a similar visitation, but because that danger has not so frequently occurred. The level of the lakes of Chălcŏ, and Xŏchĭmĭlcŏ, which are distinguished by the peculiarity of their water being sweet, instead of brackish, like that of the other three lakes, is higher by one vara and eleven inches than that of the Plaza Mayor of the Capital, and, consequently, exceeds by two varas and two feet the mean level of the waters of the lake of Tezcuco. A junction between these two lakes would, therefore, be productive of exactly the same effects, as that of the Central and Northern lakes; against which so many precautions have been thought necessary. In the great inundation, which took place before the Conquest, the history of which has been preserved by the Aztec historians, the case actually occurred, and the water rose, in the streets of Mexico, to five and six metres above its ordinary level, although not one drop of water from the Northern
