LAKES IN THE VALLEY DANGER OF INUNDATION. 179 



The valley of Mexico is a great basin, which although seven 

 thousand five hundred feet above the level of the sea, and of course 

 subject to constant and rapid evaporation, is yet exceedingly humid 

 for so elevated a region. No stream, except the small arroyo, or 

 rivulet of Tequisquiac, issues from the valley, whilst the rivers Papa- 

 lotla, Tezcoco, Teotihuacan, Guadalupe, Pachuca and Guautitlan 

 pour into it and form the five lakes of Chalco, Xochimilco, Tezcoco, 

 San Cristoval and Zumpango. " These lakes rise by stages as they 

 approach the northern extremity of the valley; the waters of Tez- 

 coco, being, in their ordinary state, four Mexican varas and eight 

 inches lower than the waters of the lake of San Cristoval, which 

 again, are six varas lower than the waters of the lake Zumpango, 

 which froms the northernmost link of this dangerous chain. The 

 level of Mexico in 1803 was exactly one vara, one foot and one 

 inch above that of the lake of Tezcoco, 1 and, consequently, was 

 nine varas and five inches lower than that of the lake of Zum- 

 pango ; a disproportion, the effects of which have been more se- 

 verely felt because the lake of Zumpango receives the tributary 

 streams of the river Guautitlan, whose volume is more considerable 

 than that of all the other rivers which enter the valley combined. 



u In the inundations to which this peculiarity in the formation of 

 the valley of Mexico has given rise, a similar succession of events 

 has been always observed. The lake of Zumpango, swollen by the 

 rapid increase of the river Guautitlan during the rainy season, 

 forms a junction with that of San Cristoval, and the waters of the 

 two combined burst the dykes which separate them from the lake 

 of Tezcoco. The waters of this last again, raised suddenly more 

 than a vara above their usual level, and prevented from extending 

 themselves to the east and south-east, by the rapid rise of the 

 ground in that direction, rush back towards the capital and fill the 

 streets which approach nearest to their own level. This was the 

 case in the years 1553, 1580, 1604 and 1607, in each of which 

 years the capital was entirely under water, and the dykes which 

 had been constructed for its protection destroyed." 2 



Such is a topographical sketch of the country accurately given 

 by a careful writer ; and to protect an important region so con- 

 stantly menaced with inundation, the viceroy now addressed him- 

 self. Accordingly he commissioned the engineer Enrique Martinez, 

 in 1607 to attempt the drainage of the lake of Zumpango, by the 



1 The level of Tezcoco is now, according to Miihlenpfordt, five feet seven inches 

 (Spanish) below that of the city of Mexico. 



2 Ward's Mexico in 1827, vol. 2, p. 282 et seq. 



