The distribution of animals and plants.  The distribution of species in the Glacial epoch was far different from that of the present.  In the glacial stages arctic species ranged south into what are now temperate latitudes.  The walrus throve along the shores of Virginia and the musk ox grazed in Iowa and Kentucky.  In Europe the reindeer and arctic fox reached the Pyrenees.  During the Champlain depression arctic shells lived along the shore of the arm of the sea which covered the St. Lawrence valley.  In interglacial times of milder climate the arctic fauna-flora retreated, and their places were taken by plants and animals from the south.  Peccaries, now found in Texas, ranged into Michigan and New York, while great sloths from South America reached the middle states.  Interglacial beds at Toronto, Canada, contain remains of forests of maple, elm, and papaw, with mollusks now living in the Mississippi basin.

What changes in the forests of your region would be brought about, and in what way, if the climate should very gradually grow colder?  What changes if it should grow warmer?

On the Alps and the highest summits of the White Mountains of New England are found colonies of arctic species of plants and insects.  How did they come to be thus separated from their home beyond the arctic circle by a thousand miles and more of temperate climate impossible to cross?

Man.  Along with the remains of the characteristic animals of the time which are now extinct there have been found in deposits of the Glacial epoch in the Old World relics of Pleistocene man, his bones, and articles of his manufacture.  In Europe, where they have best been studied, human relics occur chiefly in peat bogs, in loess, in caverns where man made his home, and in high river terraces sometimes eighty and a hundred feet above the present flood plains of the streams.

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.