Only a superficial observer can see at once that the amount of removal has been greatly in excess of the rate mentioned above. The watchman, of whom mention has been made, was in the employ of the company which constructed the road in 1854, and therefore knows where the original face of the cliff was located. At one point, where the road descends to the Clinton limestone, the whole face of the Niagara shale is laid bare. Here the shale has been removed to a distance of twenty feet from its original position, and the rocks forming the roof overhang to about that distance. Now this mass of shale must have been removed since 1854. This would require a rate of disintegration much in excess of the one assumed. Necessarily some allowance must be made for the fact that the atmospheric agencies have here had a fresh section of the shale upon which to work. Yet making all due allowance for the above condition, the rate at the mouth of the Gorge could not have been much less than that assumed above. The actual process of the enlargement has been periodic. As the falling shale undermines more and more the capping hard layers, from time to time these latter fall in immense masses. Any calculation of age based upon a few years of disintegration would be worthless; but one based upon centuries would come very near a true average. The walls of the Gorge were at first perpendicular, but as the undermining, process goes on they become sloped more and more, the falling masses forming a protection to the lower parts of the softer strata. One fact, however, to be noticed is that this protecting talus has never as yet reached so high as to stop the work of the disintegrating agencies. The horizontal distance from the water's edge back to the face of the Niagara limestone, which forms the top of the cliff, is 380 feet. On the above assumption of the rate of recession as one-fourth of an inch annually, the rate at the top of the cliff must have been about one-half inch for each year. From the observations made, it is difficult to believe that the retreat of this upper portion has been at a lower rate than a half-inch yearly; if this be true, this new line of evidence places the birth of the Niagara and the beginning of the cutting of the Gorge at Lewiston at about ten thousand years ago. [Illustration: "Maid of the Mist" under Steel Arch Bridge.]