n, 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 Cortez 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 Cortez 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.

Cortez'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 Tez