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Assuming that the cost of tunneling through the Isthmus can be executed at $10 per cubic yard, we shall have 19,762,630 dollars as the cost of one mile of tunnel. Estimating the excavation alone at present contract price, $5.40 per cubic yard for small tunnels, one mile of ship tunnel will cost $10,670,820. An open canal upon the line of the canal proposed by General Michler, uniting the Atrato with Humboldt Bay, will cost, according to the estimate of that officer, $1,792,202 per mile.
This amount, taken from the careful and elaborate estimates contained in General Michler’s report, may be assumed as a basis of comparison of the two proposed methods of intermarine communication, viz.: by uniting the two oceans upon one level by a tunnel, or by means of a moderate number of “lift-locks.” Eight locks, four at each end of the canal, or sixteen locks, eight at each end of the canal, will raise the summit fifty feet above tide in the first case, and one hundred in the second, and will cost eight millions, and sixteen millions respectively. Since two guard locks will be requisite for either method of communication (i. e. by “strait,” or canal with lift-locks), their cost should be excluded from the above sums, which are thereby reduced to six millions, and fourteen millions of dollars. These sums are fixed as the probable limits of the cost of a system of lift-locks sufficient to overcome the divide of the Isthmus, and also to supply the reader with a standard, by which he may judge of the merits of different routes.
The construction of a ship tunnel is, as has been said, “a herculean task,” and it is not apparent that “the prejudice against it will be removed by the operations at Mt. Cenis.” A moderate number of lift-locks seems preferable to a tunnel of one mile in length, which, in turn, would be more economical than an excessive number of locks. A greater number than we have mentioned may be deemed excessive.
A thorough-cut upon the level of the ocean would be a desirable method of canalization, but it seems like hampering the important design of an intermarine highway for the commerce of the world, with an impracticable condition, to insist that it should possess “absolute freedom from obstruction by lifting locks,” or that it should possess, in any degree, the “character of a strait.”
In this statement I find I have the support of M. Garella and Michel Chavalier. The opposition to the system of lift-locks appears to have originated in the objection expressed in Mr. Wheaton’s letter to Mr. Buchanan, to the large number of these structures, recommended in M. Moro’s plan for the canalization of the Isthmus of Tehuantepec.