area of country. This position for the dam was first suggested by a French engineer, Godin de Lepinay, who, in a paper read before the congress of engineers in Paris in 1879, advocated a lock canal with a dam controlling the Chagres River at Gatun. This, then, was the biggest problem peculiar to the high-level scheme, for the cutting through the "continental divide," though an even more titanic labour, would have had to be accomplished whatever type of canal had been adopted. No feature of the construction has been subject to so much criticism and anxious solicitude as this Gatun dyke. On it depends the maintenance of Gatun Lake and the supply of water for the canal. If the dam fails, everything fails. The real cause of the difficulty was the foundation upon which this big artificial hill had to be laid. The great dam at Assouan in Egypt is based upon the eternal granite, upon which masonry of natural stone is built. It is, therefore, part and parcel of the solid framework of our planet, and will probably last as long. The Gatun dam is, however, founded upon the alluvial deposits of the Chagres River. This alluvium consists of gravel firmly cemented with mud and clay, and is unquestionably water-tight. These deposits go down in places to a depth of 280 feet before the solid rock is reached. The dam had, therefore, to be laid down on the top of them. Now this foundation, though water-tight, is soft. It would have been impossible to place upon it a massive structure of rock or concrete. The deposits would have given way under its weight. The only plan was to dump down in the valley an earthen dam, making it very broad so as to distribute the weight over as large a space as possible of the alluvium underneath. A steep slope would have been impossible, for the weight of the central portion would have pushed the clay and gravel outwards, and the whole mass would have subsided. The earth-dam was to block the valley through which the Chagres had hitherto flowed uninterruptedly to the sea. This valley is a mile and a half wide, and this is, therefore, the length of the dam. Its base is 2,100 feet wide. It is 398 feet through at the surface of the water, 100 feet wide at the top, and was to be 115 feet above sea-level. The last figure has, it seems, been brought down to 104 feet, which will be an advantage, as the weight upon the foundations will be proportionately less.