ZTbe IDalles of /iDejico's Brainaae. 279 



carry the largest flow that can pass through the tunnel, or 18 cubic 

 metres, 635^ cubic feet, per second. The cutting is through a strictly 

 clay formation, comprising occasional thin strata of sand and sandstone. 



For accommodation of railroads, wagon roads, and water-courses, 

 it was necessary to construct five aqueducts four of masonry and one 

 of iron to carry rivers, four iron bridges for the passage of railroads, 

 and fourteen bridges for vehicular traffic. 



The sewage. The sewers of the City of Mexico form a network 

 of covered channels, located sometimes in the middle and sometimes 

 on the sides of the streets, these being almost always gorges, com- 

 municating with a system of secondary sewers that empty into a collect- 

 ing sewer discharging into the canal of San Lazaro, which transports 

 the sewage to Lake Texcoco. If the water is high in the lake, water 

 backs up into the sewers and saturates the soil under the houses and 

 streets. As this has been the condition for several centuries, the state 

 of the subsoil under the city can be better imagined than described. 

 The death-rate touches 40 per 1000 the highest in the civilized world. 

 Mexico's elevation of over 7000 feet is all that saves it from a pesti- 

 lence. Malarial and gastric fevers are almost continually epidemic. 



For a century the problem has been settling into one of pure sanita- 

 tion. The plans which the Government has been working since about 

 1883, though called plans for draining the valley, really seek to get a fall 

 sufficient to dispose of the sewage. In fact, in the original plan, from 

 considerations of economy, care was to be taken to keep out of the 

 projected canal all water both from the surface of the valley and from 

 the rivers. The Consulado and the Guadalupe rivers were to be car- 

 ried over the new canal in iron aqueducts. The drainage system was 

 thus to be simply a part of the sewage system of the city. 



The excavated materials have been tipped on each side of the canal 

 at their natural slopes, and a towpath near the canal level provided. 

 Sluice gates will direct the city drainage either to the canal or to Lake 

 Texcoco. A sluice gate at the junction of the smaller with the larger 

 part of the canal will control the flow of Lake Texcoco, and another 

 sluice gate will be placed at the entrance of the tunnel. 



Completion of the work. As this paper goes to press, the drainage 

 works of the Valley of Mexico are practically finished, as the waters of 

 the valley have been for several years passing through the canal and 

 the tunnel to their outlet in the river which takes them to the Gulf of 

 Mexico, and the company with whom the canal was contracted is now 

 giving the finishing touches to the sides and bottom of the canal and 

 will deliver it to the Government Board of the Drainage Directors in 

 January, 1898. It was agreed with the contractors that the portion of 

 the canal between the City of Mexico and the 20th kilometre, which is 

 comparatively easy, because the canal is not deep there, and the ex- 



