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 Cortéz.—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 Teotihuican, that have come down from a remote and highly-civilized antiquity.
THE ANCIENT LAKES.
The valley of the city of Mexico, which lies to the south of these hills, is also of an oval shape, but is not more than twenty miles in extent. The surface-water with which it is saturated is in part fresh, and in other parts tequisquite; that is, where the waters have a current, they are fresh; but where they remain from year to year discharging their volume only by evaporation, then they become infused with the saline properties of the soil,[31] ] and all about them is marked with barrenness. If the process of evaporation was less intense than it is,[32] ] all vegetation would die from the extreme humidity of the soil; as the gardener's phrase is, it would rot. Even in the city of Mexico itself, a couple of feet of digging in its alluvial foundation brings you to the water-level in the dry season, and seventy or eighty yards of boring does not carry you beyond the perceptible influence of tequisquite.[33] ] The effects of this law of evaporation puzzled the Aztecs, who were, of course, ignorant of all philosophical principles, and could only account for the disappearance of the immense mass of water that fell in the valley in the wet season, upon the hypothesis that the Tezcuco had a leaky bottom, or that there was a hole in the lake—an idea that thousands in Mexico credit to the present day. This was the origin of that absurd story which Cortéz repeats in his letters, that this lake communicated with the sea, and had its daily tides.
There could not have been a much greater volume of water in this marshy valley in the time of Cortéz than at present, if the whole accumulations of each year were to be carried off by evaporation alone from so small a surface as is here presented for the sun to act upon. But as the volume of water is the turning-point in the history or fable of the conquest, I must adduce the proofs and arguments that are at hand to establish this statement. The level of the water could not have been higher, it is clear, for in that case neither Mexico, Mexicalzingo, or Iztapalapan could have been inhabited.
Cortéz's account of deep waters has often been made plausible by adding the hypothesis that the accumulating mud of centuries has filled up the lakes, so that they now are only shallow ponds. But this by no means removes the difficulty, for then, as now, the waters of the southern laguna flowed into Tezcuco, conveying with them the infinitesimal infusion of tequisquite that had instilled itself into the Chalco. Had the volume of Chalco and Xochimulco been increased several feet, then the slight Indian barriers and the long grass would no longer have been able to retard the progress of the water till evaporation had diminished its quantity, but, precipitating itself in a mass into the Tezcuco, it would have overwhelmed the town of Tezcuco and all other villages upon the shores, and established an equilibrium of surface in the two ponds.
All the lagunas, canals, and ditches that have been described are navigated by small scows that draw but a few inches of water, which are the medium of an extensive internal commerce. Through the lagunas and canal of Chalco come from Cuatla all the supplies of the products of the hot country for the city and surrounding region. This commerce exceeds the whole foreign trade of the republic.[34] ] This kind of boat was probably introduced by Cortéz, and in this convenient form his thirteen brigantines were probably made; for, had his brigantines been of a larger draught of water, they could not have navigated canals intended only for Indian canoes. One of these vessels, when supplied with a sail, a cannon, and a movable keel or side-board, would be a formidable auxiliary in an assault upon the city at the present day. And if one such scow was placed in the ditch on each side of the southern causeway, as Cortéz alleges, it would enable an assailing enemy to present just so much more front as the additional width of two boats would give him.
THE CAUSEWAYS AND CANALS.
Writers have expressed their surprise at the existence of two navigable canals to each causeway, one on either side, as an immense expenditure of unnecessary labor. The explanation of this is found in the fact that in the construction of a pathway (for Cortéz says that it was only 30 feet in width) through wet and marshy ground, a broad ditch is ordinarily made on either side to obtain earth for the embankment, and to keep the water-level permanently below the top of the pathway. So it is, and so it must always have been at Mexico, in order to keep these foot-paths in traveling condition. In the dry season, which is the winter, these broad ditches are covered with floating islands of green "scum;" but in the rainy season, which is the summer, they may be navigated by the shallow Mexican scows. A pathway of earth thirty feet in width could not endure the winds and waves of a navigable lake, or the wear and "swash" of a canal twelve feet deep on either side; and the fact that Cortéz navigated the ditches in the rainy season establishes the insignificant size of his famous brigantines.