THE PANAMA ROUTE FOK A SHIP CANAL. 547 



Levees, or protective eijihankments, would iilso l>e rcMiuired on the 

 same side of the eanfll between Bohio and (latiui. the C'hag'res River 

 leaving' the canal line at the latter point on its way to the sea. 



The principal (Migineering feature of the entire route is found at 

 Bohio; it is the grc^it dam across the Chagres Rixer at that Point, 

 forming Lake liohio, th(^ sunnnit level of the canal. The new Panama 

 Canal Company located tiiis dam at a point about 17 mil(>s from Colon, 

 and designed to make it an earth structure suitably pa\-ed on its faces, 

 but without any other masonry feature. Some borings had been made 

 along the site, and test i)its were also dug by the Fi'ench engineers. 

 It was the conviction of the Isthmian Canal (Jommission, however, 

 that the character of the pi'oposed dam might be affected l)y a further 

 examination of the subsurface matei'ial at the site. Consecjuently the 

 boring' parties of the Conmiission sunk a lai'ge mnnbei' of ))ore 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 m-aterial below the ))ed and l)anks 

 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 th(» French site the 

 bed rock at the deep(\st point is 143 feet below sea level, with large 

 masses of per\'ious and semipervious sand, grayel, 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 

 tilled with sand, gravel, and (day, irregularly distributed and with all 

 deg-rees of admixture, large masses in all cases being of open texture 

 and pervious to water. The site adopted by the Conmiission for the 

 purposes of its plans and estimates is located nearly half a mile down 

 the course of the rivm- from that selected by the New Panama Canal 

 Company. The geological valley is nearly 2,000 feet wide at this loca- 

 tion, but the deepest rock disclosed b}' the borings of the Conmiission 

 is but 128 feet below sea levcd. The actual channel of the river is not 

 more than 150 feet 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 feet above the river 

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

 compacted clay and sand, and rises equally as a])ru})tly 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 ratlun* remarkable uni- 

 formity of elevation extends for about 1,200 feet in a southw^esterly 

 direction to the rocky hill in which the Bohio locks would be located. 

 The rock slope on the easterl}^ or northerly baidv 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 feet below 

 sea level. 



