Suffice it to say, that by this means a constant outlet was made for the lake of Zumpango, the highest of the five, and for the Rio de Guatitlan, a stream which formerly ran into it.
So much for one cause of the change in the present appearance of the city.

Then the Spaniards were great cutters down of forests.

They rather liked to make their new country bear a resemblance to the arid plains of Castile, where, when you arrive in Madrid, people ask you whether you noticed _the tree_ on the road; and moreover, as they wanted wood, they cut it, without troubling themselves to plant for the benefit of future generations.

Now, when the trees were cut down, the small plants which grew in their shade died too, and left the bare earth to serve as a kind of natural evaporating apparatus.

And, between these two causes, it has come to pass that the extent of the lakes has been so much reduced, and that Mexico stands on the dry land--if, indeed, that may be called dry land, where you cannot dig a foot without coming to water.
During the Tertiary period the whole valley of Mexico was one great lake.