45© THE POPULAR SCIENCE MONTHLY. 



In the last days of November the water usually rises to eight me- 

 tres above the ordinary level. In the valley of the Chagres the an- 

 nual rainfall is 3 metres. The average discharge of the river during 

 the wet season is 134 cubic metres per second, and 6G6 during the 

 floods. In the exceptional rise of 1879 it reached 1,930 cubic metres, 

 but it must be reraenibored that such discharges seldom last more than 

 forty-eight hours ; for, as Lieutenant Kimball states in his valuable 

 report just published, "The floods are of short duration, showing that 

 they result from large local rainfall, and not from extensive water- 

 shed," When the barrage and derivations are completed, I believe 

 that the problem of the Chagres will be solved. 



Another interesting feature of this division is the two aqueducts 

 that will be built near Emperador to carry the waters from the mount- 

 ain valleys on the northern and eastern side across the canal into the 

 Obispo liiver. Their elevation will be the present levels of these sites, 

 and vessels will pass under them. The bed of the cuttings at the end 

 of the division have now a level of 55 metres. 



The original elevation of the Culebra in the plane of the axis of 

 the canal was 108 metres ; the cuttings have reduced it to 78 metres. 

 The width of the cut at the summit is 300 metres, the slope of the 

 sides being forty-five degrees. But a serious question at this point 

 lies in the accumulation of material by wash, land-slides, and fissures. 

 Last year 78,000 cubic metres of earth fell into the canal. The hill 

 on the right side of the cut is formed of dolerite and sand, and no 

 wash or slip can occur from it. But on the left side I found strata 

 of clay covered with a mixture of alluvium, sand, and conglomerate. 

 During the wet season this deposit becomes saturaited, and the in- 

 creased weight, coupled with the dip of the strata, causes it to slip 

 oA^er the smooth surface of the clay into the canal. The clay in turn 

 contracts during the dry season, fissures result, and hence another 

 source of land-slides ; and the natural wash of torrential rains is a 

 third cause of deposit in the bed of the cut. 



But a far more serious problem apparently is the annual movement 

 of this side toward the axis of the canal. It varies from 12 to 18 

 inches, and the contractors acknowledge that its remedy may require 

 heavy expenditure for increased slope, if nothing more. As yet, how- 

 ever, this can not be regarded as an actual danger. The removal of 

 so much material from the Culebra must affect the position of the 

 center of gravity of the mass, and it may be that this movement results 

 from a settling to the new conditions. This is the more hopeful view, 

 and a reasonal»le one, but there is greater cause to fear that this is a 

 movement of the whole hill-side, and not an earth-slide from the higher 

 portions of the bank. The clay of Culebra is of the same bed as the 

 " greasy " or slip])ing clay of the adjoining section of Paraiso. Refer- 

 ring to the latter, Lieutenant Kimball says its movement "in some 

 places carries one bank almost intact across the cut with the top sur- 



