To the times we have just passed in review succeeded others of a very different kind, to which has been given the general naive of Neolithic. The fauna, probably lender the influence of climatic and orographic changes, underwent a complete transformation; the mammoth, the cave-bear, the megaceros, and the large felidæ died out, the hippopotamus was no longer seen, except in the heart of Africa; the reindeer and other mammals that love to frequent the regions of perpetual snow, retired to the extreme north; and in their place appeared our earliest domestic animals, the ox, the sheep, the goat, and the dog. Man, who witnessed these changes, continued to progress; he abandoned his nomad for a sedentary life; he ceased to be a bunter, and became an agriculturist and a shepherd. Everywhere we meet with traces of new customs, new ideas, and a new mode of life. This progress is especially seen in the industrial arts. Metals it is true are still unknown, but side by side with tools, which are merely chipped or roughly cut, we find for the first time hatchets, celts, small knife-blades, and arrow-heads admirably polished by the long-continued rubbing of one stone on another. Polishers, so much worn as to bear witness to long service, are numerous in all collections, and rocks and erratic blocks retain incisions which must have been used for the same purpose.6 It is impossible to enumerate the number of polished hatchets which have been found; their number is simply incalculable. Of all of them, however, those of Scandinavia are the most remarkable for delicacy of workmanship. With the fine hatchets of Brittany, may be compared the blades found at Volgu, and preserved in the Museum of Copenhagen, and those in pink, gray, and brown flint, from the Sordes Cave in the south of France; but we cannot fix the date of the production of any of them. One of the great difficulties of prehistoric research, a difficulty not to be got over in the present state of our knowledge, is to distinguish with any certainty the periods into which an attempt has been made to divide the life-story of man from his first appearance upon earth.