It will be noticed that in the dam proper there is no core of masonry or puddled chalk or clay whatever. It was at one time intended that there should be. I have alluded to the alarmist rumours that were raised again and again at Panama and created much uneasiness in the United States. These were especially concerned with the great dam, and that word must have frequently been on the lips of the engineers in more than one significance. Every possible test was applied to determine the exact character of the underlying materials, to ascertain whether there was any connection between the swamp areas to the north and south through the deposits in the gorges which the earthwork was to bridge, to prove the ability of the material below to support the structure, and to find out whether suitable material for the dam could be found in its neighbourhood. "As the result of all these investigations," wrote Colonel Goethals,[15] "it may be briefly stated that the underlying material is impervious to water; that it possesses ample strength to uphold the structure that will be placed upon it, and, the subsoil being impervious, that there is no connection between the swamps above and the sea below." In order to make assurance doubly sure, Colonel Goethals planned the dam so as to include triple interlocking steel sheet-piling across the valley, driven down to bedrock, and decided to carry the dam to a height of 135 feet. Even so, the news of a collapse was wired home, and this so impressed President Roosevelt that he sent a commission of engineers to the isthmus accompanied by President-elect Taft. The investigations had a different result from what had been expected. Instead of being dissatisfied with the size and strength of the dam, the engineers declared that it was being built too high and that the steel piling was unnecessary. It must be admitted, therefore, that the efficiency of the Gatun dam has been subjected to the most rigorous tests, and that no further anxiety on the subject need be felt.