CHARACTERISTICS AND DISTRIBUTION OF LAKES 561 
ceased to be a lacustrine city, and many of the surrounding swamps 
disappeared ; but irregularities in the level of the lake, and the 
stagnation of sewage waters, made the town very unhealthy. A plan 
of drainage for remedying this state of affairs was begun in 1607 
under the direction of Enrico Martinez, but for various reasons it 
was not carried out successfully, and in 1629 the city was overwhelmed 
by a disastrous flood. Of the 20,000 families who had their homes 
in the city, only 400 survived. For a time it was thought that 
Mexico should be abandoned, and that Puebla should be made the 
capital in its stead ; but the plans of drainage were carried on for 
years without much method, and Mexico still held her position as 
capital of the country. The canals of drainage were not completed 
till towards the end of the nineteenth century, and were then not 
carried through the old cuttings, but were formed farther to the east. 
This desague, as the work is called, is the greatest drainage system 
and one of the most remarkable engineering enterprises in the world. 
It consists of a canal 43 miles in length, and a tunnel somewhat 
exceeding 6 miles, and it carries off the surplus waters of the whole 
Mexican basin into the River Tequizquiac, a tributary of the Tula, 
whence they flow by the Rio Panuco into the Gulf of Mexico. Partly 
as a result of this draining off of the waters of the lake, and partly 
as a result of a general desiccation of the surrounding regions, the 
lake has withdrawn, till now over two miles intervene between the 
lake-shores and the city. 
The other inland drainage area lies north of the volcanic high- 
land, and has been termed the Chihuahuan province of the great 
American desert, in contradistinction to the Sonora Nevada province 
to the west of the Western Sierra Madre. The lakes of this province 
are all of the ephemeral desert type. During the rainy season the 
waters which find no seaward outlet are collected in depressions on the 
plateaus, where extensive tracts, known as lagunas, remain flooded for 
several months at a time. But the waters are rapidly reduced in 
level by evaporation, and fluctuate greatly with the quantity of 
rainfall. At a very early period, when the rainfall of the country 
was greater, there was, according to Reclus,^ an excess of water, 
which found its v^ay to the course of the Rio Grande del Norte 
by valleys, where it is still possible to follow with the eye the old 
river-beds. Then, as precipitation became less, the outflow ceased, 
and the waters of the basins thus cut off gradually became salt. 
Many lakes have been entirely dried up, owing to the fact that 
the streams which fed them were lost through evaporation in the 
desert before reaching them. One reason given for this process 
of desiccation is the reckless destruction of the upland forests by 
^ Le Mexique au debut du xx^ siecle, p. 55, Paris, n.d. 
36 
