Page:Popular Science Monthly Volume 10.djvu/220

208 computation, cannot be placed at less than 3,000 or 4,000 years before the time at which they were thus brought to light. Cuvier endeavored to ascertain, by a very just and proper method, what foundation there was for the belief in a gradual and progressive change of animals, by comparing the skeletons and all accessible parts of these animals, such as crocodiles, birds, dogs, cats, and the like, with those which are now found living in Egypt, and he came to the conclusion—a conclusion which has been verified by all subsequent research—that no appreciable change had taken place in the animals which inhabited Egypt. And he drew thence the conclusion, and a hasty one, that this fact was altogether opposed to the doctrine of evolution. The progress of research since Cuvier's time has furnished far stronger arguments than those which he drew from the mummified bodies of Egyptian animals. A remarkable case is to be found in your own country in the neighborhood of the magnificent falls of Niagara. In the immediate vicinity of the whirlpool, and again upon Goat Island, in the superficial deposits which cover the surface of the soil of the rock in those regions, there are found remains of animals in perfect preservation—shells belonging to exactly the same forms as at present inhabit the still waters of Lake Erie. It is evident from the formation of the country that these animal remains were deposited in the beds in which they occur, at the time at which the lake extended over the region in which they are found. This involves the necessity that they lived and died before the falls had cut their way back through the gorge of Niagara; and, indeed, it is possible to determine that at that time the falls of Niagara must have been at least six miles farther down the river than they are at present. Many computations have been made of the rate at which Niagara is thus cutting its way back. Those computations have varied greatly, but I believe I am speaking within the bounds of prudence if I assume that the tails of Niagara have not retreated at a greater pace than about a foot a year. Six miles, speaking roughly, are 30,000 feet; 30,000 feet, at a foot a year, are 30,000 years; and we are fairly justified in concluding that no less a period than this has passed since these shell-fish, whose remains are left in the beds to which we have referred, were deposited. But there is even still stronger evidence of the long duration of certain types than this. As we work our way through the great series of the Tertiary formations, we find species of animals identical with those which live at the present day, diminishing in numbers, it is true, but still existing in a certain number in the oldest of the Tertiary rocks. And not only so, but when we examine the rocks of the Cretaceous epoch itself, we find the remains of some animals which the closest scrutiny cannot show to be in any respect different from those which live at the present time. That is the case with one of the lamp-shells, a Terebratula which is found in the chalk, and which has continued as it was found, or with insignificant variation,