REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


 Mr. WALLACE. I only intend it to be a minimum figure, and my thought in these figures I submitted to you was all along the lines of an endeavor to be on the conservative side.
 Mr. RANDOLPH. You estimate 3 miles of track for every shovel, .do you not, Mr. Wallace?
 Mr. WALLACE. Approximately,.yes. That includes main tracks, storage tracks, dump tracks, and everything in the nature of a railroad track that is dependent upon the number of units that are at work.
 Mr. HUNTER. There is one other question, Mr. Chairman, that I would like to put to Mr. Wallace. It is in respect to your estimate of the cost of material, which, after adding 10 per cent, you suggest is 60 cents all around. Have you considered or can you give any figures that you have estimated for the cost of pumping per cubic yard of the cutting, supposing a sea-level canal is going to be constructed? We are considering two projects, a sea-level project and a lock-canal project. In the sea-level project, have you formed any estimate of what the additional cost will be per yard for pumping? That is not included, as I understand from your figures.
 Mr. WALLACE. No, sir. I left that out for two reasons. First, it was utterly impossible to make any computation of that kind, that is, except in a most general way, and I thought my other figures were large enough to absorb any reasonable amount of that. Again, something I have not referred to in those papers, if I were doing that work myself, as an engineer in charge of the work or as a contractor, I would consider as a possible plan the excavation in the dry to 40 feet below sea level of one central ditch or channel, simply wide enough to admit of the passage of my dredges and vessels, and I would do the rest of my widening-that is, below sea level-in the water.
 Mr. HUNTER. Would you not encounter, by proceeding with the work in that manner, a difficulty which must be met in days to come, when the canal prism will be widened, in the way of protective works where you are working under water? That is the great difficulty we always experience when we are blasting rock under water, particularly in a case of this sort, when, as you said yourself, the material is very mixed in its character. Some parts of it may have to be protected, some may not have to be protected, probably only a very small proportion of the cut may have to be protected; but how would you proceed with that protective work if you complete a section of the cut under water?
 Mr. WALLACE. That is one of the difficulties; so, of course, doing it under water is an alternate plan that is to be determined. In my mind I thought the determination of that question should be left until we reached that point in the actual progress of the work. Now, there are places there where, if it were necessary to treat in some special manner, it might be necessary to cofferdam off that particular part in order to put in a retaining wall or in order to treat the slope.
 Mr. HUNTER. That would be a very serious matter, to cofferdam to the rock foundation, with a head of water of 40 feet.
 Mr. WALLACE. The probabilities are you would not have to construct your wall the entire depth of 40 feet. It would depend entirely on circumstances.
 Mr. HUNTER. You might not have to, or, on the other hand, you might have to protect the lower part of the side of your cutting and not the upper part.
 Mr. WALLACE. 1 do not think it would be probable that you would have to go to the full 40 feet below sea level before you would determine that question, and if you did not have to go to that depth, then you could cofferdam off. You might only have 10 feet of water to cofferdam in and you might have 20. On work with which I have been connected I have seen cofferdams put in the Mississippi River in a current of 5 or 6 miles an hour, on the Rock Island Rapids, in 20 or 25 feet of water, and done cheaply. With the proper appliances it is not a very difficult thing to do. Your area would be very small, because in that case you would take your whole canal section and build your dams right across the canal. I do not imagine there would be a case where you would want to do that after you had excavated your full 40-foot channel. I think before you got down to that depth you would have a comparatively moderate depth through which to sink your test pits or take your borings; that you would be able to determine accurately the character of your material before you would excavate that part, and could arrange for it by other means. That is, I mean you could build your cofferdams before you go down there, or you could let


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