=The present rate of recession.=—There are various sketches, more or less accurate, made in the early part of the nineteenth century, and from the later period there are daguerreotypes, photographs, and maps, which refer especially to the Canadian Fall; and which, taken together, render possible a comparison of the earlier with the later brinks. By comparing the earliest with the recent, views it is seen at a glance that the Falls are receding, and at a quite appreciable rate (Fig. 382). A careful comparison of the maps made in 1842, 1875, 1886, 1890, and 1905 of the brink of the Canadian Fall (Fig. 383) indicates that for the period covered the rate of recession has been about five feet per year, and similar studies made of the American Fall show that it has been receding at the rate of only three inches per year, or one twentieth the rate of the recession of the Canadian Fall. [Illustration: FIG. 383.—Map to show the recession of the brink of the Canadian Fall, based upon maps of different dates (after Gilbert).] =Future extinction of the American Fall.=—It is because of this many times more rapid recession of the Canadian Fall that the Niagara cataract, instead of lying athwart the gorge, enters it from its side. The Canadian Fall is thus in reality swinging about the American, and the time can already be roughly estimated when this more effective drilling tool will have brought about a capture, so to speak, of the American Fall through the cutting off of its water supply. It will then be drained and left literally “high and dry”, an enduring witness to the geological effect of an island in making an unequal division of the waters for the work of two cataracts. As already pointed out, the inefficiency of the American Fall as an eroding agent is amply attested by the wall of blocks already appearing above the water below it. The tourist who a thousand years hence pays a visit to the Niagara cataract, provided the water flow is allowed to remain as it has been, will find above this rampart of blocks a bare cliff in part undermined, and surmounted by a nearly flat table surface which is cut off from the existing cataract by a higher section of the gorge (Fig. 384). It is quite likely that this table will furnish the most satisfactory viewpoint of the future cataract of that date. [Illustration: FIG. 384.—Comparison of the present with the future falls.]