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PHYSICAL CHARACTERISTICS OF THE CANAL ROUTE
While the size and character of the canal were open questions, the general location was determined. The line of cut adopted by the French had been selected by some of the early exploiters; the Panama Railroad had been located in the same valleys and depressions; and the French had actually begun to build along this line. At this point it is well to consider briefly the character and topography of the canal route and adjacent territory as it was before any work was done, but bearing the future canal in mind.
The Isthmus of Panama, if it joined the two continents by the shortest line, would extend northwest toward North America and southeast toward South America; but it does not follow the shortest line, and on the map looks as if South America had been pushed northwestward and the narrow part of the Isthmus on the end toward South America had been bent out of shape with a bulge to the north and the concave side to the south, almost forming a semicircle enclosing the Gulf of Panama. (See plan No. 1.) Near the head of this gulf is an indentation known as the Bay of Panama. This bay touches that part of the rough semicircle where the Isthmus sweeps to the northeast toward the top of the semicircle, and where a line at right angles to the Isthmus is about northwest. This northwest line from the Bay of Panama ends in the Limon Bay, on the Atlantic side, and happens to pass through the region where the Continental Divide is much lower than anywhere else and where the Isthmus is less than 36 miles wide, only 5 miles wider than at the very narrowest point. The line if slightly distorted may be made to pass for three-fourths of its length along the valley of the Rio Grande River on the Pacific side, and the valley of the lower Chagres on the Atlantic side, except that the Chagres before reaching Limon Bay turns off to the left to its mouth, seven miles west of the bay, while the line continues straight to Limon Bay. This is in general terms the course of the canal.
Limon Bay faces almost directly north, and has an opening three miles wide into the Caribbean Sea, and extends five miles inland of the full width. The depth of the water varies from 5 feet to 36 feet. (See plan No. 2.) The Atlantic end of the French canal was cut through the swamps along the east shore of Limon Bay and extended into the bay, so as to make use of Colon as a protection from northerly seas. Limon Bay, on the westerly and inland sides, is surrounded by much higher land, except that the lowlands of the small Mindi River valley extend inland from the above-named swamps almost through the ridge, which is here very low. The narrow strip of lowland continues inland beyond the Mindi River valley and dips into the Chagres valley near Gatun. One would almost have expected the. Chagres River to seek outlet straight ahead in Limon Bay, only three miles distant; but the little ridge between the Chagres and the headwaters of the Mindi River prevented this, and so the Chagres follows the lowlands behind the ridges surrounding Limon Bay and discharges into the Caribbean Sea about seven miles west of the bay. At Gatun, where the line of the canal first meets the Chagres, the valley is about a mile and a half wide, but as we follow upstream it becomes very much wider. The stream is sluggish and winds in and out amongst the swamp lands.
Just above Gatun the Chagres on its right bank receives an important tributary, the Gatun River. It was of some importance in the plans for any canal of which the sea-level portion extended inland beyond Gatun, for the canal had either to cross the river, to take its flow, or otherwise the river must be turned off before reaching the canal by a new channel or diversion to the sea parallel to the canal. The French actually built a very wide diversion to the sea, 8 miles long. The Trinidad River enters the Chagres from the other side, about three miles above Gatun.
Throughout this portion of the Chagres the watersurface is but little above sea level, and it so continues inland as far as Bohio, 16 miles by the canal line from Colon. At Bohio the valley contracts, and this was the site selected for the locks and dams in the French canal, and in one of the early American plans. The land surface from Bohio upstream becomes gradually more undulating and the slopes of the valleys become steeper. At Bas Obispo, 13 miles inland from Bohio by canal line, or 29 miles from Colon, the low water level of the river rises to 45 feet above the sea. Up to this point the Chagres valley leads in a fairly direct line toward the Pacific Ocean, and fortunately approaches the low point of the Continental Divide. Now the canal line must leave the Chagres, for the river makes an abrupt turn, and to follow it to its sources would carry us into the mountains to the northeast, that is, into the apex of the roughly semicircular part of the Isthmus. The canal builder cannot dismiss the river from his mind at the point where the line of the canal leaves the valley, for some of the most important problems of the canal are dependent upon the character of the stream above Obispo.
At Bas Obispo the Chagres River is joined by its tributary, the Obispo River, the valley of which offers the best opportunity for continuing the canal for the next 4 miles. The continental ridge begins at Bas Obispo, and with it the hills become higher. The stream is tortuous, and the canal line cannot follow it, but must be cut on more direct lines to avoid objectionable curvature.
The elevation of the ground is constantly increasing, reaching a low summit at Empire, and the highest summit at Culebra, where the future canal passes between Gold Hill and Contractors Hill. The highest elevation of the ground on the center line is 312 feet above sea level, but the highest part of the sloping sides will be 554 feet above sea level. Culebra is about 6 miles from Obispo, and about 35 miles from Colon. The country falls much more rapidly on the Pacific side, and 3 miles beyond Culebra, close to