696 Mr. A. Henry Savage Landor [June 18, 



have been bored. Water has been found in some of the bore-holes ; in 

 others it overflowed the casing. The pressure of artesian flows in the 

 valley, which was fully expected, does not necessarily mean that the 

 dam will be endangered by them if the necessary precautions to safe- 

 guard its stability are taken — precautions which are ordinary with 

 the principles of earth-dam construction. According to American 

 engineers, the geological sections at right angles to the axis of the 

 Gatun Dam, as well as to the three sections parallel with the dam 

 axis, conditions seem rather against a tendency to a free under- 

 ground flow. It is believed that at Bohio or Gamboa there is not a 

 sufficient elevation in the valley of the Chagres river to force an 

 appreciable body of water through the alluvial deposits at Gatun. 

 The inclination is to believe that there is merely a level hydraulic 

 grade line between Gatun and Bohio — this, of course, on the sup- 

 position that there is a free underground connection between the two 

 places. The velocity of the flow under such conditions could but be 

 slight ; for, were it not, on reaching the narrows of Gatun, it might 

 prove destructive to the underlying and easily dissolved strata. 



It is, perhaps, on the surface of the rock that are found the most 

 pervious conditions. The rocks are seamed and jointed, conducting 

 the water to the bottom of the gorges, where it remains under 

 pressure. 



There seems to be no indication of a continuous underground 

 flow parallel with the current in the Chagres Valley, or else deposits 

 of continuous gravel should have been found in the borings. More- 

 over, a careful investigation has failed to establish any continuous 

 underlying water-bearing stratum. The water found below the 

 surface of the valley derives its pressure, it has been ascertained, 

 from the hills surrounding the valley. The layer most to be feared, 

 on account of its watei'-bearing capacity, is a stratum of sandy clay 

 relatively near the surface. 



Allowing that the wall of masonry below the foundations of the 

 dam will effectively prevent the underground flow from passing 

 below these foundations and eroding them in time, it still remains to 

 be seen whether the water may not still find a passage by fissures in 

 strata further down. No doubt American engineers have given full 

 attention to this point. 



There was one point which I personally feared more than any 

 other. It was whether the hills surrounding the lake would actually 

 keep the water in place, or whether they would let it escape through 

 their fissured mass. 



Colonel Goethals seems to think that the hills will not leak. He 

 states that the question has been thoroughly studied. The reservoirs, 

 he says, constructed in the hills of the same geological formation do 

 not show the slightest signs of leakage. I am not prepared to judge 

 whether that reasoning would hold good for the larger lake. 



Whether the Americans build " the Straits of Panama " or a lock 



