to the Arabs as "Pharaoh's beans;" and these organisms stand out in high relief on the weathered portions of the Great Sphinx. Some of the oldest things in the world in their relation to human history,--erections, many of which had survived the memory of their founders even in the days of Herodotus,--are formed of materials so modern in their relation to the geologic epochs, that they had no existence as rock until after the Palæozoic and Secondary ages had gone by. Not only the Carboniferous sandstone of the High Church and Parliament House of Edinburgh, but even the Oolitic (that is, Portland stone) of Somerset House and St. Paul's, are of an antiquity incalculably vast compared with the stone out of which the oldest of the pyramids were fashioned. [Illustration: Fig. 116. NUMMULITES LÆVIGATA. (_Pharaoh's Beans._)] The second example which I shall adduce is one with which many of my auditors must be already familiar. The Falls of Niagara are gradually eating their way through an elevated tract of table-land, upwards towards Lake Erie, at the rate of about fifty yards in forty years; and it has been argued by Sir Charles Lyell, that as they are now seven miles distant from Queenston, where the elevation of the plateaux begins, they must have taken about ten thousand years to scoop out their present deep channel through that space.[43] Ten thousand years ago the Falls were, he infers, at Queenston; and the grounds on which he reasons are exactly those on which one would infer that a laborer who had cut a ditch two hundred yards long at the rate of ten yards per day, and was still at work without pause or intermission, had begun to cut it just twenty days previous. A reverend anti-geologist takes up Sir Charles;[44] and, after denouncing the calculation as "a stab at the Christian religion," seeing it involves the assertion that the "Falls were actually at Queenston four thousand years before the creation of the world according to Moses," he brings certain facts, adduced both by other writers and Sir Charles himself, to bear on the calculation, such as the fact that the deep trench through which the Niagara runs is much narrower in its lower than in its upper reaches, and that the river must have performed its work of excavation, when the breadth was less, at a greatly quicker rate than now. And thus the work of excavating the trench is brought fairly within six thousand years. Nor is the principle of the reasoning bad. In our illustration of the ditch excavated by the laborer we of course take it for granted that it is a ditch of the same depth and breadth throughout, and excavated in the same sort of soil; for if greatly narrower and shallower at one place than at another, or dug in a greatly softer mould, the rate of its excavation at different times might be very different indeed, and the general calculation widely erroneous, if based on the ratio of progress when it went on most slowly, taken as an average ratio for the whole.