In order to understand the development of early man, we should know that prehistoric peoples are ranked according to the materials of which their tools were made and the skill shown in their manufacture. There are thus four well-marked stages of human culture preceding the written annals of history:     4 The Iron stage.     3 The Bronze stage.     2 The Neolithic (recent stone) stage.     1 The Paleolithic (ancient stone) stage. In the Neolithic stage the use of the metals had not yet been learned, but tools of stone were carefully shaped and polished. To this stage the North American Indian belonged at the time of the discovery of the continent. In the Paleolithic stage, stone implements were chipped to rude shapes and left unpolished. This, the lowest state of human culture, has been outgrown by nearly every savage tribe now on earth. A still earlier stage may once have existed, when man had not learned so much as to shape his weapons to his needs, but used chance pebbles and rock splinters in their natural forms; of such a stage, however, we have no evidence. [Illustration: Fig. 372. Paleolithic Implement from Great Britain] =Paleolithic man in Europe.= It was to the Paleolithic stage that the earliest men belonged whose relics are found in Europe. They had learned to knock off two-edged flakes from flint pebbles, and to work them into simple weapons. The great discovery had been made that fire could be kindled and made use of, as the charcoal and the stones discolored by heat of their ancient hearths attest. Caves and shelters beneath overhanging cliffs were their homes or camping places. Paleolithic man was a savage of the lowest type, who lived by hunting the wild beasts of the time. Skeletons found in certain caves in Belgium and France represent perhaps the earliest race yet found in Europe. These short, broad-shouldered men, muscular, with bent knees and stooping gait, low-browed and small of brain, were of little intelligence and yet truly human. The remains of Pleistocene man are naturally found either in caverns, where they escaped destruction by the ice sheets, or in deposits outside the glaciated area. In both cases it is extremely difficult, or quite impossible, to assign the remains to definite glacial or interglacial times. Their relative age is best told by the fauna with which they are associated. Thus the oldest relics of man are found with the animals of the late Tertiary or early Quaternary, such as a species of hippopotamus and an elephant more ancient than the mammoth. Later in age are the remains found along with the mammoth, cave bear and cave hyena, and other animals of glacial time which are now extinct; while more recent still are those associated with the reindeer, which in the last ice invasion roamed widely with the mammoth over central Europe. [Illustration: Fig. 373. Paleolithic Sketch on Ivory of the Mammoth]