The ice-sheet was not permanent during its stay. Twice, and perhaps three times, it somewhat capriciously retired to the far north, disappear ing rather suddenly, and then slowly creeping down again into latitudes which we now call temperate, freezing them with the cold of an Arctic winter which knew no summer. The comparatively mild periods between these visitations are called the "Inter-glacial periods." First Appearance of particular interest that these geologic events have to us in this connection is that it was either immediately before, during, or else immediately after this Glacial period that man first appeared on the earth, or at least it is in the strata of this age that we find the first unequivocal traces of his presence. Some, indeed, have maintained that evidence of his handiwork has been taken from strata of the Miocene period, but the most careful writers on the subject have not as yet con ceded that this is established. There is, moreover, an inherent improb ability from analogy that any one species has maintained so complex an organism as man's for so long a period. The evidence that assigns him an appearance on earth in the Inter-glacial or the immediately Post-glacial period has received the sanction of the most eminent geologists.
But when we speak of "man" as then existing, that word must be understood in its 'widest sense, embracing any animal which had the faculty of building a fire and fashioning ever so rude a tool or weapon from a piece of stone ; for that was all the ability that we can assign to those very early representatives of our species. It is not likely that they had any religious sentiments or that they were capable of articulate speech. An intellectual status as low as this appears to be indicated by the remains of their art and of their bony skeletons which have been discovered. A brief description of these ancient relics will illustrate this.
The Earliest Stone of the earliest specimens of man's ingenuity are of stone ; some few are of bone. Doubtless, he at that time also made use of wood, but his works in that material soon perished. The stones lie chose were of a size convenient to hold in the hand, and it seems probable that the hands of these primitive mechanics were smaller than ours, about the size of a boy's. The pieces of flint and argillite selected were rudely chipped by striking one against another, and thus brought to an edge and point. In this form they would serve as a more effective weapon, tool, or utensil, for all of which purposes doubt less they were intended. Frequently one side or one end only is chipped, the others being left in the natural state. Such instruments are called "hand-stones," or cells. The chips flaked off in their preparation have also been collected, sometimes in considerable quantity, showing that the manu facture of these implements was carried on with diligence (pl. 1, fig. to).
Use of evidence proves that these first settlers knew the use of fire. Flints are found that have been subjected to the fire for the
purpose of breaking them into small and angular pieces, and even the charcoal and ashes of some of these ancient hearths have been exhumed in deposits which competent geologists place as remote in time as the Inter-glacial epochs. In and around the remains of these early camp fires the bones of animals, some of extinct species, broken to extract their marrow or artificially sharpened to a point, indicate that these primitive tribes were hunters and fishers, that they cooked their food, and that they had some beginnings of a social life.
Drift and Cave earliest tool- and fire-using animals, who are generally included in the species man, although undoubtedly much inferior to any tribe now known to us, are called distinctively the "River drift" and "Cave" men, because their relics are found for the most part in the beds of drift gravel deposited in the ancient river-beds of various streams, as the Ouse in England and the Somme in France ; and also in the caves of France, Belgium, England, and other countries, where they have continued undisturbed and covered with the deposits of later forma tions. By some writers the Drift men are considered an older generation than, or even a different race from, the Cave men, but this is not gener ally accepted.
This inceptive period of human art is called the Palaeolithic or " Old Stone " age, or the period of rough stone implements, the characteristic feature of its remains being that they are of rough, unpolished stone, the simple art of smoothing and sharpening one stone by rubbing it against another being unknown or indifferent to these workmen (p1. 1, fig. 12).
Their most remarkable fact about these Drift men was their extremely wide dispersion over the earth's surface, and conse quently the great length of time that they must have lived upon the globe. They must have been very ill provided with means of travelling, as they had no domestic animals and probably no boats ; yet their charac teristic relics have been disinterred from the caves and river-valleys of Western Europe, from the old gravel-beds of Palestine and Upper Egypt, from the laterite formations at the foot of the Ghaut Hills in Southern India, at a depth of forty feet below the surface in the diamond-diggings at the Cape of Good Hope, at an equal depth under the Post-glacial gravels near Trenton on the Delaware River in New Jersey, in the deposits on the upper terrace of the Mississippi north of St. Paul, a hundred feet below the surface in the auriferous gravels of California, in the Drift and Glacial deposits of Chili and Buenos Ayres, and else where. Collections taken from these various localities offer so few differ ences in the specimens that but for the character of the material used they might be attributed to any one of the list.