THE PANAMA ROUTE FOR A SHIP CANAL. 263 



a further examination of the sub-surface material at the site. Conse- 

 • l in nt I v the boring parties of the commission sunk a large number of 

 bore holes at six different sections or possible sites along the river in 

 the vicinity of the French location. These borings revealed great 

 irregularity in the character and disposition of the material below the 

 bed and banks of the river. In some places the upper stratum of 

 material was almost clear clay, and in other places clear sand, while 

 all degrees of admixture of clay and sand were also found. At the 

 French site the bedrock at the deepest point was found 143 ft. below sea 

 level, with large masses of pervious and semi-pervious sand, gravel, and 

 mixtures of those materials with clay. Apparently there is a geological 

 valley in the rock along the general course of the Chagres River in this 

 vicinity filled with sand, gravel and clay, irregularly distributed and 

 with all degrees of admixture, large masses in all cases being of open 

 texture and pervious to water. The site adopted by the commission for 

 the purpose of its plans and estimates is located nearly half a mile 

 down the course of the river from that selected by the new Panama 

 Canal Company. The geological valley is nearly 2,000 ft. wide at this 

 location, but the deepest rock disclosed by the borings of the commis- 

 sion is but 128 ft. below sea-level. The actual channel of the river is 

 not more than 150 ft. wide and lies on the extreme easterly side of 

 the valley. The easterly or right bank of the river at this place is clean 

 rock and rises abruptly to an elevation of about 40 ft. above the river 

 surface at ordinary stages. The left or westerly bank of the river is 

 compact clay and sand and rises equally as abruptly as the rocky bank 

 of the other side, and to about the same elevation. From the top of the 

 abrupt sandy clay bank a plateau of rather remarkable uniformity of 

 elevation extends for about 1,200 ft. in a southwesterly direction to 

 the rocky hill in which the Bohio locks would be located. The rock 

 slope on the easterly or northerly bank of the river runs down under 

 the sandy river bed, but at such an inclination that within the limits of 

 the channel the deepest rock is less than 100 ft. below sea-level. 



After the completion of all its examinations and after a careful 

 study of the data disclosed by them, the commission deemed it advisable 

 to plan such a dam as would cut off absolutely all possible sub-surface 

 flow or seepage through the sand and gravel below the river surface. It 

 is to be observed that such a sub-surface flow might either disturb the 

 stability of an earth dam or endanger the water supply of the summit 

 level of the canal or both. The plan of dam finally adopted by the com- 

 mission for the purposes of its estimates is shown by the accompanying 

 plans and sections. A heavy core wall of concrete masonry extends 

 from bed rock across the entire geological valley to the top of the struc- 

 ture, or to an elevation of 100 ft. above sea-level, thus absolutely closing 

 the entire valley against any possible flow. The thickness of this wall 



