The Valley of Mexico is a flat plain, in the lowest portion of which the City of Mexico is situated, two or three miles from Lake Texcoco. The plain consists of lands barren and lands cultivated, marshes and swamps, all intersected by numerous streams falling into the lakes, as well as irrigation and drainage canals, whilst on the rising ground which appears in places the volcanic understructure is laid bare, often in the form of great lava sheets. The group of lakes have been elsewhere described in these pages. Lake Texcoco, whose shores are now distant from the city, is a dreary waste of brackish water with scarcely any fish-life, inhabited by water-fowl at certain seasons. During the period of overflow its rising waters cover many added square miles of ground, but in the dry season the water recedes, leaving saline-covered marshes of desolate aspect. Lakes Chalco and Xochimilco, however, are very different in their regimen and aspect. They are of fresh water, and stand at an elevation some 10 feet higher than Texcoco, into which they discharge. Fertile meadows surround these, and Xochimilco is now, as it was at the time of the Conquest, a "Field of Flowers," which is the meaning of its native nomenclature, not unworthy of the designation of an "earthly paradise," which the modern Mexicans bestow upon it. [Illustration: THE VALLEY OF MEXICO: THE GREAT DRAINAGE CANAL.] The position of the City of Mexico near Lake Texcoco, which receives the waters of all the other lakes of the system, has ever rendered it liable to inundation, and to a saturated and unhealthy subsoil, conditions which, were it not for the healthy atmosphere of the bracing uplands whereon the valley is situated, would undoubtedly make for a high death-rate. The drainage and control of the waters of the valley have formed matters of thought for Mexico's successive Governments for more than four centuries. Work to this end was begun under Montezuma in 1449, nearly three-quarters of a century before the Conquest. During the colonial _regime_ further works were undertaken, in 1553, to replace those destroyed by Cortes, followed by other works in 1604 and 1708. But only after the Republican _regime_ was established was the work carried to completion, upon a plan brought forward by a Mexican engineer. These works, which were mainly carried out during the closing years of last century by English firms of engineers and contractors,[28] consist of a canal and tunnel. The canal is thirty miles long, flowing from the city and bearing its sewage and storm-waters, and taking the overflow from Lake Texcoco: and discharging thence into a tunnel, perforating the rim of the valley, about six and a half miles long. This in turn empties into a discharge conduit and a ravine, and the waters, after having served for purposes of irrigation and for actuating a hydro-electric station, fall into an affluent of the Panuco river and so into the Gulf of Mexico. This work,