gates swing together and the ship is imprisoned in a chamber 1,000 feet long and 110 feet wide and built of concrete. In a moment the water in this chamber begins to rise, being supplied through holes in the bottom, and the ship rises with the water.

Fifteen minutes after entering the lock, the ship has risen with the water for 27 feet. If the full capacity for filling the lock should be used the ship would rise that height in eight minutes. Another set of gates swing open in front of the ship, and the locomotives tow it into the second lock, a concrete chamber of the same dimensions. The gates having closed behind, this chamber begins filling with water until the ship is raised again for 27 feet. A third set of gates open and the ship is towed into the final lock where the operation is repeated with a raise of 30 feet, or a total lift for the three locks of 85 feet. When the gates in front swing open the ship steams out into the Gatun Lake. The time spent in climbing 85 feet was an hour and a half.

For sixteen miles through this lake the ship steams in a channel 1,000 feet wide; for four miles in a channel 800 feet wide, and for three miles in a channel 500 feet wide, or twenty-three miles in all. Then it enters the famous Culebra cut, which is 300 feet wide through the continental mountain divide, and nine miles long. At the end of the Cut is the Pedro Miguel lock, thirty-two miles from Gatun.

After entering this lock, which essentially is the same as the ones on the Atlantic side, the ship goes through the reverse of the process at Gatun. The

water in the concrete chamber begins falling, taking the ship down with it. When it has fallen 30 feet the gates in front open and the ship goes out into another artificial lake, a mile and a half long, at the end of which are the Miraflores locks. These two locks lower the ship 27 feet each, or a total for the three locks of 85 feet, which was the height the ship was raised on the other side. The ship then steams through a sea-level channel for seven miles to the Pacific, having made the whole journey from deep water in the Atlantic to deep water in the Pacific, fifty miles, in ten hours.

Thus it will be seen that the Atlantic and Pacific oceans are still separated by thirty-two miles of land at Panama, on which is a fresh-water lake 85 feet above sea-level. The locks simply are so many stairsteps up to and down from this lake. At both ends the locks are built in pairs, or twins, so that ships going in opposite directions may pass through them simultaneously. A wall 60 feet thick separates the locks, and if one set should become disabled, the adjoining set still would be available for passage. The time required for a ship to mount the three locks on one side and descend the three locks on the other side is three hours.

On the Atlantic side, the locks at Gatun are connected and constitute one solid piece of masonry. On the Pacific side the lock at Pedro Miguel is separated from two locks at Miraflores by a small lake a mile and a half long. This lake, like the great Gatun Lake, is formed by damming rivers. A dam at the Pedro

Miguel lock, which is the first lock encountered going toward the Pacific, holds the waters of Gatun Lake from spilling down the Pacific slope.

Chief Engineer Stevens began the excavations in the Gatun and Pedro Miguel lock sites in 1906, shortly after the decision was made for a lock-type canal, but most of the excavation and all of the concrete laying has been done under Col. Goethals. It was necessary to remove about 5,000,000 cubic yards of rock and earth from the site of the three locks at Gatun to prepare a foundation for the tremendously heavy structure. Careful borings had been made to ascertain if a suitable foundation could be found there.

On August 24, 1909, the first concrete was laid in the Gatun lock site. Rock of a desirable kind for use in making the concrete, as well as sand, could not be found in the Canal Zone, and experiments along the coast showed that at Porto Bello, twenty miles East of Colon, good rock could be quarried, and sand was discovered in suitable quantities and quality at Nombre de Dios, forty miles East of Colon. These two places are the oldest on the Isthmus, Columbus having been there in 1502.

Rock crushing began at Porto Bello on March 2, 1909. If all the rock and sand removed from Porto Bello and Nombre de Dios was placed in barges separated by the usual distances in a tow, they would reach from Colon to New Orleans, or 1,500 miles. This material was towed to Colon and thence through the old French canal to Gatun. Here it was unloaded