Page:Vol 6 History of Mexico by H H Bancroft.djvu/686

666 being to determine, in the most absolute manner, if it was practicable to construct a ship-canal across the Isthmus of Tehuantepec.

Any scheme contemplating to feed the canal from other than natural sources of supply should be considered impracticable; though in the case of failing to obtain a natural supply, studies and calculations might be made, in order to expose the degree of difficulties to be encountered in obtaining an artificial supply by means of collecting reservoirs and pumping.

On the other hand, if the solution of this problem should present no extraordinary difficulties, or obstacles that could not be overcome with the ordinary appliances of engineering skill in its present state of development, I should declare the project practicable, unless the expense to be incurred in its construction should appear palpably incommensurable with the importance of the undertaking.

The data obtained from our explorations and surveys prove that a shipcanal is practicable on the Isthmus of Tehuantepec, because the difficulties to be encountered in its construction are of the ordinary type, or such as are inherent to works of a similar nature, with the difference that they will be met on a larger scale. This fact is due to the assumed dimensions of the canal, and is inherent to the conception of the project, in whatever part of the world it might be located.

The nature of the Isthmus of Tehuantepec makes it impossible to construct across it a 'through-cut' canal. The use of locks becomes indispensable in order to reach the summit-height at Tarifa. This point is the lowest and most available pass in the mountains traversing the isthmus from east to west.

Its true mean elevation above the Pacific Ocean is 754.4 feet, as given by the spirit-level. This height can be easily diminished to 732 feet by a cut 22 feet in depth on the Tarifa Pass. In this manner, the summit-reach of the canal will have the same elevation as the Tarifa River, upon the point at which the summit-level will be fed with water.

The only point from which the canal can be fed is from the Upper Coatzacoalcos or Corte River, near its junction with the Blanco. At this place the Corte delivers 1,618 cubic feet of water per second, and the surface of the water in the driest season is 660 feet above the ocean, or 72 feet below the summit-level of the canal.

Three miles up stream from this point the Corte's waters ascend to the summit-level height.

The river Blanco yields 120 cubic feet per second, and is four feet above the summit at the Tarifa Pass. The banks and bed of the Corte are of clay, rocks, feldspar, and granite. The direction of the stream, width of its bed, which is free from gravel, and the topographical features of the locality, are admirably constituted for the erection of a dam. The materials are at hand, and of the most durable nature.