The diagrams attached hereto show the enormous difficulties that have just been referred to in a much more graphic way than any mere description could do. It will be observed from the illustration (p. 298) that the Rio Chagres crosses the course of the canal no fewer than five times in little more than five kilometres, and that the Rio Obispo also steps in to add to the complications of the situation. On the San Pablo section again, within a distance of three kilometres, the river crosses the line of canal three times. The Chagres river, which is so great an obstacle in the project of the Panama Canal, rises on the western slopes of the Cordilleras, and runs through a broken and irregular country, to the north of the auriferous granite hills which branch off to Cruces and Gorgona. This river and its affluents is said to drain an area of about 1550 square miles.[193] From Matachin, where the Panama canal parts company with the valley of the Chagres, to the sea, there is a total distance of twenty-eight miles, in the course of which the river falls about 35 feet.[194] The rain of a single day is said to raise the waters of the Chagres from 35 to 40 feet, and below Matachin there is a cataract of 50 to 60 feet. It was part of the project to abandon at this point the valley of the Chagres, and to cut through the Cordilleras. The level of the bottom of the canal is here 100 feet below that of the bed of the Chagres, or 140 feet below the mean level of the nearest indicated points on the section of the plans above and below the intersection. In a length of nine miles, at the foot of the ascent of the Cordillera at Matachin, the lowest point is 166 feet, and the highest 333 feet above the bed of the canal. A tunnel of 7720 metres in length was at one time proposed to be cut through this section, but M. de Lesseps stood out for a cutting _á ciel ouvert_, and it has been remarked that according to the plans there has been an assumption that the sides of this vast cutting will stand so nearly perpendicular as to slope only one foot horizontal in every ten feet vertical. In a dry climate, with good firm clay or rock, this might not involve difficulty or danger, but the climate of Panama is exposed to a tropical rainfall. A rainfall of six or seven inches in a few hours is not uncommon.