382 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


 There i,3 one remark I should like to make about slides. A slide with 50,000 or 100,000 cubic yards of material in it looks like an enormous one, but when you consider the proportion of that slide to the entire work in the excavation, it is simply a minor detail.
 Mr. STEARNS. I did not get any expression of opinion when onl the ground as to the slide, except that mny informants thought it had to come out, as it was already moving; and as I understood this case, they were not cutting into the foot of the clay where the slide occurred except as it came into the canal section over the edge of the rock and was obstructing the tracks in the canal section.
 Mr. WALLACE. That particular slide, I think, could be helped by drainage. There is practically a spring or vein of water that comes down there. You understand how those slides work. It is necessary to understand what is underneath them. The basaltic rock is on a very steep inclination toward the Pacific, and then there are places in the rock where there seem to have been ravines. The clay would fill up these ravines and would follow the ravines down into -the excavation. We had a slide there that came down one of those small ravines last winter, if you recollect, Mr. Chairman, and I do not think there was over 15,000 or 20,000 yards of it, but it stopped our work absolutely at the time. That was about a year ago; but it was due to the fact that the tracks lapped each other and the excavator on one track was south of the slide, and on the other track north. All trains had to pass the point, and the slide came down and cut off access to the excavation in both directions; but that was due to the old arrangement of the tracks. They had not been changed up to that time. That was about a year ago now, if I remember correctly, in September, 1904.
 The CHAIRMAN. Yes; I remember it. It occurred also, I think, at a point where the stratification changed. There was a radical difference in the material just on that dividing line.
 Mr. STEARNS. My question was whether such slides could be stopped or whether they would continue to slide and have to be taken care of.
 Mr. WALLACE. The question of slides is one that should be of less importance every year that the work goes on, if the material is properly handled in the dry season.
 Mr. STEARNS. You would advise taking it off for a certain distance back on the rock?
 Mr. WALLACE. Yes.
 Mr. STEARNS. In the dry season, as I understand?
 Mr. WALLACE. Yes.
 Mr. STEARNS. Will that stop it, or would it also need drainage?
 Mr. WALLACE. That depends altogether on the conditions that would be developed at each point. Of course the cause of these slides is the fact that clay, a soft material, is lying imposed on an inclined surface of hard material. The clay becomes saturated, and the surface of this hard material becomes lubricated by the saturation, and the weight of the saturated material, of course, helps to assist in the movement. Now, where you have that at a point where there is anything in the nature of a ravine or a depression in the original foundation, and water is following it similar to a subterranean or submerged stream of water, the case is still further aggravated. At this particular point where the slide occurred there has always existed a spring. If that spring and stream of water can be cut off, of course you remove one of the difficulties.
 Mr. STEARNS. My question is whether you thought it could be.
 Mr. WALLACE. Yes; I think it could.
 Mr. RANDOLPH. There is a spring at the head of that slide, and the French company had three tanks there. They seemed to have used it as a water supply.
 Mr. WALLACE. It goes without saying that the farther away from the point of the slide you can take and divert the water the better, of course.
 Mr. WELCKCER. Mr. Wallace, in one of your papers that has been read this morning you say that the condition of the sea bottom at La Boca is just the same as in Limon Bay, if I understood it correctly.
 Mr. WALLACE. Not exactly the same, but I said there were places where the same conditions occurred. That is, there are places where there are large masses of mud at both localities.'
 Mr. WELCKER. That is a factor of great importance in relation to the dredging that would


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