quisquite_) pond of Tezcuco, having received as a
tributary the canal of Tacubaya, which passes along the southern
boundary of the city.

THE LAKES OF THE VALLEY.

The highest water of the valley of the city of Mexico is the pond of
Chalco, in the extreme southeast, being 4-8/12 feet above the level of
the Grand Plaza of the city, and 20 miles distant therefrom, and
11-2/12 feet above Tezcuco;[29] but its volume being small for the last
400 years, the slight impediments of long grass and a few Indian dikes
have prevented any injury to the city by a too rapid flow to the
northward. Xochimulco is the pond, or open space in the marsh, that
extends from the Chalco to near Mexicalzingo. Tezcuco is the lowest
water in the valley, being 6-1/2 feet below the Grand Plaza of the
city.[30] It receives the surplus of the waters that have not already
been evaporated in the other ponds. At this great elevation, 7500 feet,
evaporation does its work rapidly all over the valley, but it is in
Tezcuco that the residuum of the waters is deposited.

[28] Report of M. L. Smith, Lieutenant of Topographical
Engineers, United States Army.

[29] Lieut. Smith's Report.

[30] Ibid.

CHAPTER XV.

The two Valleys.--The Lake with a leaky Bottom.--The Water could not
have been higher.--Nor could the Lagunas or Ponds have been much
deeper.--The Brigantines only flat-bottomed Boats.--The Causeway
Canals fix the size of the Brigantines.--The Street Canals.--Stagnant
Water unfit for Canals.--The probable Dimensions of the City
Canals.--Difficulties of disproving a Fiction.--A Dike or Levee.--The
Canal of Huehuetoca.--The Map of Cortez.--Wise Provision of
Providence.--The Fiction about the numerous Cities in and about the
Lake.

It may be well here to repeat that, strictly speaking, there are two
valleys of Mexico--the upper northern valley, and the valley of the
city of Mexico; the first extends in an oval form to the north of the
hills of Tepeyaca, some sixty miles, and communicates with the plains
of Otumba and Apam. In this valley are the two ponds, or _lagunas_, of
Zumpango and San Cristobal, the highest waters of Mexico; and in it
also is the half of the Tezcuco, which is the lowest laguna of the
valleys. It is a country of fine farming lands, and was probably
inhabited long before the time of the arrival of the Aztecs in the
lower valley, as I infer from its proximity to the extensive ruins of
Teotihuica