So much at present for the Chagres problem. The other main feature of the isthmus is met with about the point where the river suddenly changes its direction--that is at Bas Obispo, or Gamboa, about nine miles from the Pacific outlet. Here are the hills, the backbone or "continental divide," averaging over 300 feet high but rising to much higher points, which connects the Cordilleras of South with the Sierras of North America. For eight or nine miles the canal must run through this central barrier on its way to the Pacific. The earliest French notion was for a ship tunnel--a project perhaps never seriously contemplated. The only other course was to cut right down through this hilly country. That was a tremendous undertaking, which required, even for its inception, a good deal of the faith which is said to be able to "remove mountains." We shall look more closely at the famous "Culebra Cut" when we come to the American canal. Most of the work of the French companies consisted of the dredging of the sea-level channels at the Atlantic and Pacific ends. But they drove a pretty deep furrow as well through the Culebra Mountains, excavating in all about 22,600,000 cubic yards. With their sea-level scheme the French had, of course, a bigger proposition before them at the hills than their American successors. They would have had to cut right down below sea-level, whereas the bottom of the cut in the American lock-canal is forty feet above that level. Considering the difficulty the United States engineers have had with "slides" and "breaks" along the sides of their cutting, one suspects that the much deeper and narrower channel of the French would have proved impracticable. The French scheme gave a width to the channel at this point of only 74 feet, while the bottom width of the American canal is 300 feet. The French work at the "Cut" was all utilizable by the Americans, who, though with different machinery, adopted the same general method of excavation.