cuco, 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 Cortez, 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 Cortez 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 Cortez 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