72 



SCIENCE. 



[N. S. Vol. XXIV. No. 603. 



isthmus, making two natural sea-level sec- 

 tions, one about eighteen miles long on the 

 northerly side of the isthmus, and the other 

 about seven miles long on the southerly- 

 side; that on the northerly side running 

 for the greater part of its length generally 

 along the course of the Chagres River. 

 This river has been one of the main fea- 

 tures in the consideration of the canal work 

 since the beginning of operations by the old 

 Panama Canal Company in 1881. It is not 

 a large river, as it has not more than about 

 800 square miles of watershed above Bohio, 

 where in its flow toward the sea it leaves 

 the rising ground and enters what may be 

 termed the coastal plain, through which 

 it meanders along a sinuous course to the 

 ocean. It has even changed its course 

 in the past at various locations in this 

 marshy ground. 



That portion of the canal route lying in 

 the higher ground of the divide is but about 

 24 miles long, and but little more than three 

 quarters of a mile of it had an original 

 surface elevation exceeding 200 feet. The 

 surface material is largely clay of ordinary 

 character, slippery and easily moved when 

 vret, but holding well in place when pro- 

 tected from the entrance of water. Below 

 this covering of clay lies material of irregu- 

 lar character, as the entire isthmus is of 

 volcanic origin. In the continental divide, 

 at a depth varying from twenty to forty 

 or fifty feet below the surface, an indurated 

 clay, classed for purposes of excavation as 

 soft rock, is found. This material gives 

 place irregularly to hard rock at greater 

 depths. Much of the rock of the isthmus 

 is soft, although there is hard basalt in a 

 number of places and, in one locality on 

 the Panama slope of the divide, columnar 

 basalt is found. 



The work performed by the old and new 

 Panama Canal companies amounted in the 

 aggregate to not far from eighty million 

 cubic yards of all classes of excavation, of 



which possibly forty million cubic yards 

 at most will be found available for the 

 American construction of the canal, 

 whether a lock plan or a sea-level plan be 

 adopted. This work extends practically 

 over the entire canal route, with the ex- 

 ception of the approach channels in the 

 two terminal harbors, and it is nearly con- 

 tinuous. Over considerable stretches of 

 the higher ground it is little more than 

 shallow cuts through the softer surface 

 materials, but at the great Culebra cut 

 the material which has been excavated 

 varies from the surface clay, readily re- 

 moved by steam shovels, to hard basaltic 

 rock, requiring blasting by high explosives 

 before it can be removed. All the ma- 

 terial, even the indurated clay, below the 

 softer covering, requires blasting before it 

 can be excavated, although the softer por- 

 tions need the action of black powder only. 



Except the deep cutting at Culebra, 

 through the summit of the continental 

 divide, the most marked work done by the 

 old French company was the dredging 

 through the low marshy lands from Colon 

 to Bohio. There is at present a strip of 

 partially completed canal about 14 miles 

 long with a bottom width of seventy-two 

 feet, which may be navigated by vessels 

 drawing twelve to fourteen feet, with the 

 exception of a short distance near Colon. 

 Indeed, so much excavation was completed 

 in this portion of the canal, intersecting 

 the Chagres at a number of places, that 

 the waters of that river have abandoned 

 the old bed and now flow through the par- 

 tially completed canal prism. 



In the execution of any plan of canal 

 one of the principal problems involved is 

 the control of the Chagres River during 

 seasons of flood. This problem has been 

 considered so formidable in the past that 

 some experienced engineers have hazarded 

 the opinion that the Panama Canal could 

 never be successfully completed in conse- 



