210 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


 Within those limits and with such precautions an earth dam is completely safe and a satisfactory solution, but to consider an earth dam having a water head three times greater is something which I can not contemplate for a definite and perpetual structure. I concur with the first Isthmian Canal Commission in thinking that at Bohio even an altitude of 92 -feet could not be admitted without the supplementary security of a core wall; but I would not go any further even with the best core wall.
 I may be considered as overtimorons, but in technical art, when no calculations are able to satisfy me, I do not consider such lack of boldness as a fault.
 Second. Its erection across the bed of a violent, unruly stream, without having, as we have at Bohio, a bed of the same level and of the same cross section through which it may be deflected, seems to me will be attended by innumerable difficulties and condemned to certain failure. The absence of a wide and deep bed into which the river may be deflected while the depositing of the earth of the dam is going on in the dried site of the dam, is a great objection to the construction of a dam anywhere but at Bohio. It applies to Gamboa; but it applies also to Gatun, where an earth dam has been sometimes proposed without paying sufficient attention to the conditions of the site.
 Third. The great apparent advantage of an earth dam is the possible employment of the vast mass of material to be excavated from the central massif but this advantage vanishes like the mist in the sun when you come to consider the nature of the material to be extracted.
 There is not, among all kinds of earths, one which is more unqualified for such a purpose. The earth employed in a dam must be of such nature that all its particles come into close contact with one another, leaving no room between them for the water to pass. This contact can be obtained with a suitable soil either by mechanical compression, or, much better, by a good method of handling the suitable ground. Neither by compression nor by any other system will any adherence ever be obtained for the particles of the spoils of the great cut.

CHARACTERISTIC FEATURES OF THE INTERNAL ELEMENTS OF THE CULEBRA CUT-MANY ERRORS COMMITTED ABOUT THIS SUBSTANCE.

 It consists of rock in limited proportion, of hard rocky clay, of argillite for the greater part, and of some softer clay near the surface of the ground.
 There have been many opinions expressed about this argillite, this rocky clay, of the great cut. Many errors have been committed about its stability. 'In fact, it is a hybrid material, and some see it as a rock, others as clay. In reality it is a soft rock which, while in place, with the necessary amount of internal moisture, is, under or above the water, perfectly hard. Under water, it is absolutely stable; above water it may weather somewhat, but in insignificant proportions so long, I repeat, as it is not taken away from its natural position. But if we take a piece of this clayish rock and expose it to the atmosphere it loses its water, the molecules separate f rom one another, and it falls into separate particles, as lime does when it comes in contact with the humidity of the air. If you put a desiccated piece of this clayish rock in water it falls into pieces.
 Many very distinguished minds have been curiously misled about it, over and over again. I have heard that rocky clay called soluble clay several times. Some have entertained the most unfounded fears about the action the water would have on the sides of a cut opened through this substance.
 NO WALLS AT CULEBRA ARE NECESSARY.

 Even the Comit6' Technique was a victim of that error, and projected walls in the Culebra section to protect this so-called soluble clay from the contact of a supposed solvent.
 In reality, these walls never have to perform such part; and, by the way, it is well to say that if the eminent engineers of the Isthmian Canal Commission retained these walls in their project, it was not in the minds of several of them to protect the clay against the water, but to protect the ships against accidental contact with some protuberance. Mr. Noble and Mr. Morison stated that fact to me, and in the writings of General Hamns the same opinion may be inferred.


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