In substance the Canal works consist, first, of an enormous dam (at Gatun), which holds up the water of the river Chagres so as to flood a valley twenty-four miles long; secondly, of a channel—­nine miles in length—­(the Culebra Cut)—­which carries the valley on through a range of low hills; and, thirdly, of a set of locks at each end of this stretch of water that are connected by comparatively short approaches with the sea.  The surface of the lake will be from 79 to 85 feet above sea-level, and vessels will be raised to this height and lowered again by passing through a flight of three locks upward and another flight of three locks downward.  The passage of both flights of locks is not expected to occupy more than three hours, and ships should complete the transit of the Isthmus—­a distance of about fifty miles—­within twelve hours at most.  The design of the work offers nothing that is new in principle to engineering science.  Dams, cuttings, and locks are familiar contrivances.  But they are on an immensely larger scale than anything which has previously been attempted.  The area of the lake of impounded water will be 164 square miles, and it has been doubted whether the damming of so large a mass of water, to a height of 85 feet, could safely be undertaken.  But this portion of Central America is apparently not liable to earthquakes.  And the dam is so large as to be a feature of the earth’s surface.  It is nearly half a mile broad across its base, so that although its crest is 105 feet above sea-level its slope is not very perceptible.  Its core is formed of a mixture of sand and clay, poured in from above by hydraulic processes.  This has set hard, and is believed to be quite impervious to water at a much higher pressure than that to which it will be subjected.  In the center of the river valley—­a mile and a half broad—­across which the dam has been flung, there very fortunately arose a low rocky hill.  This is included in the dam, and across its summit has been constructed the escape or spill-way.  During seasons of heavy rain the surplus discharge of river water will be very heavy, and a cataract will pour over the spill-way.  But it will rush across a bed of rock, and will be unable to erode its channel.  And it will be employed to generate electrical power which will open and shut the lock-gates and generally operate the Canal machinery.  The river Chagres will energize the Canal as well as fill it.

The locks are gigantic constructions of concrete.  Standing within them one is impressed as by the mass of the Pyramids.  The gates are hollow structures of steel, 7 feet thick.  Their lower portions are water-tight, so that their buoyancy in the water will relieve the stress upon the bearings which hinge them to the lock-wall.  Along the top of each lock-wall there runs an electric railway; four small electric locomotives will be coupled to a vessel as it enters the lock approach, and will tow it to its place.  The vessel will not use its own steam.  This will