From the flow of rivers we have a gigantic measure of geological time. It is supposed that the Falls of Niagara were once at Queenstown, and that they have gradually worn their way back in the living rock, for a distance of seven miles, to the place where they now pour their thunders. An ingenious English geologist, a high authority in his science, Sir Charles Lyell, assuming that this retreat might have been at the rate of one foot a year, shows that the cataract must have poured over that rock for a period of at least 36,960 years. And the same authority teaches us that the alluvion at the mouth of the Mississippi, the delta formed by the deposits of that mighty river (here let it be remarked that alluvions and sand-banks are the most recent geological formations on the surface of the earth, being nearest to our own age), could not have been accumulated within a shorter period than 100,500 years.[263] Even this term, so vast to our small imagination, is only one of a series composing the present epoch; and the epoch itself is but a unit in a still grander series. These measurements, adopted in this branch of knowledge, can be little more than vague approximations; but they teach, from the lips of Science, as perhaps nothing else can, the infinite ages through which this globe has already travelled, and the infinite ages which seem to be its future destiny. [263] Lyell's Principles of Geology (7th ed.), Vol. I. p. 216. Lyell's Travels in North America, Ch. 2. Horner's Anniversary Address, for 1847, before the London Geological Society, pp. 23-27. D'Archiac, Histoire des Progrès de la Géologie, Tom. I. p. 358. Thus we stand now between two infinities,--the infinity of the Past, and the infinity of the Future; and the infinity of the Future is equal to the infinity of the Past. In comparison with these untold spaces before and after, what, indeed, are the six thousand years of human history? In the contemplation of Man, what littleness! what grandeur! how diminutive in the creation! how brief his recorded history! and yet how vast in hopes! how majestic and transcendent in the Future!