Page:Popular Science Monthly Volume 10.djvu/607

Rh Prof. Marsh in the Western cretaceous and tertiary beds. It remains but to add a link to the genealogy of the horse, discovered by Prof. Marsh since the time when Prof. Huxley lectured. You will remember that Prof. Huxley showed that there was a regular series of progressive forms from the Eocene Orohippus to the recent horse, in the character of the teeth, and in the structure of the fore and hind feet. There was more than that, perhaps, when we consider that there was an increase in size, in length of limb, and consequent activity, of the animal. In the Orohippus we have four toes on the front and three on the hind limbs, and so far Prof. Huxley was able to trace the genealogy of the horse with its single toe down toward the type of mammals with five toes. But we can now go a little further in the process of the evolution of the horse. In New Mexico, in a fossil bed, the horizon of which is below that in which the Orohippus occurs, Prof. Marsh has found the remains of an animal which he calls the Eohippus. The feet, which are very much like those of the Orohippus with their well-developed four toes in front and three behind, show a rudiment of the outer or fifth toe. The Eohippus was an animal as large only as a fox, though perhaps a little stouter, and, from the structure of its limbs, is the nearest yet discovered progenitor of the horse to the usual five-toed mammalian type. And in his lecture Prof. Huxley anticipated the actual discovery of the Eohippus by showing that such a form must have existed as the progenitor of the four-toed horse. Animals, also, which were the prototypes of the camel, have been there discovered by Prof. Cope. Strange if, at the time when the whole earth presented such a profusion of vertebrate life, man should not also have appeared upon the scene! The conditions were never so perfect, either before or since. Over this field of luxuriant life, the cold broke in. The ice commenced to form, and then to move in masses, scattering or extirpating the plants and animals. There were migration and adaptations. Such animals and plants as could adapt themselves to the cold persisted. To probably smooth skinned elephantoid types, the woolly mammoth succeeded in the northern regions. Stunted willows replaced tree-like plants of the same botanical family. If it met man, it must equally have modified his habits of life and his physical characteristics. It must have made something like an Esquimaux of him. As to the cause of the glacial epoch itself, from a study of all that has as yet been said on the subject, we must ascribe it to upheavals of land in the north, and a change, perhaps a consequent change, in the earth's position toward the sun. There was, it seems, an elevation of the earth's crust and a variation in the earth's axis; which latter, in order to have produced the climatic effects of former geological periods, must apparently have been more nearly perpendicular than it now is. It is probable that oscillations then set in, which may make a second glacial epoch probable, although of this we cannot speak with certainty. Evidence is