The one greatest undertaking of the whole excavation was the Gaillard Cut. Work had been in progress on this since 1880, and during the French control over 20,000,000 cubic yards were removed. On May 4, 1904, when the United States took charge, it was estimated that there was left to excavate 150,000,000 cubic yards. Some idea of the size of this big cut may be formed from the fact that this division has within its jurisdiction over 200 miles of five-foot-gage track laid, about fifty-five miles of which is within the side slopes of the Gaillard Cut alone. Gatun Dam. The great dam at Gatun is a veritable hill--7,500 feet over all, 2,100 feet wide at the base, 398 feet through at the water surface, and 100 feet wide at the top, which is 115 feet above sea level. The dimensions of the dam are such as to assure that ample provision is made against every force which may affect its safety, and while it is made of dirt, a thing before unheard of, it is of such vast proportions that it is as strong and firm as the everlasting hills themselves. Fluctuations in the lake due to floods are controlled by an immense spillway dam built of concrete. The front of the dam is the arc of a circle 740 feet long with fourteen openings which, when the gates are raised to the full height, permit a discharge of 140,000 cubic feet per second. The water thus discharged passes through a diversion channel in the old bed of the Chagres River, generating, by an enormous electric plant, the power necessary for operating the locks. The locks of the canal are in pairs, so that if any lock is out of service navigation will not be interrupted, also, when all the locks are in use the passage of shipping is expedited by using one set of locks for the ascent and the other for descent. These locks are 110 feet wide and have usable lengths of 1,000 feet. The system of filling adopted consists of a culvert in each side wall feeding laterals from which are openings upward into the lock chamber. The entire lock can be filled or emptied in fifteen minutes and forty-two seconds when one culvert is used and seven minutes and fifty-one seconds, using both culverts. It requires about ten hours for a large ship to make the entire trip through the canal. Meeting all Emergencies. Many extraordinary feats of engineering were accomplished to overcome the difficulties presented. Special contrivances, wonderful in their operation, were invented to meet exigencies and emergencies.