At the close of the Tertiary period, from causes not yet determined, the Northern Hemisphere underwent a great depression of temperature.  From a torrid it passed to a glacial condition.  After a period of prodigious length, the temperature again rose, and the glaciers that had so extensively covered the surface receded.  Once more there was a decline in the heat, and the glaciers again advanced, but this time not so far as formerly.  This ushered in the Quaternary period, during which very slowly the temperature came to its present degree.  The water deposits that were being made required thousands of centuries for their completion.  At the beginning of the Quaternary period there were alive the cave-bear, the cave-lion, the amphibious hippopotamus, the rhinoceros with chambered nostrils, the mammoth.  In fact, the mammoth swarmed.  He delighted in a boreal climate.  By degrees the reindeer, the horse, the ox, the bison, multiplied, and disputed with him his food.  Partly for this reason, and partly because of the increasing heat, he became extinct.  From middle Europe, also, the reindeer retired.  His departure marks the end of the Quaternary period.

Since the advent of man on the earth, we have, therefore, to deal with periods of incalculable length.  Vast changes in the climate and fauna were produced by the slow operation of causes such as are in action at the present day.  Figures cannot enable us to appreciate these enormous lapses of time.

It seems to be satisfactorily established, that a race allied to the Basques may be traced back to the Neolithic age.  At that time the British Islands were undergoing a change of level, like that at present occurring in the Scandinavian Peninsula.  Scotland was rising, England was sinking.  In the Pleistocene age there existed in Central Europe a rude race of hunters and fishers closely allied to the Esquimaux.

In the old glacial drift of Scotland the relics of man are found along with those of the fossil elephant.  This carries us back to that time above referred to, when a large portion of Europe was covered with ice, which had edged down from the polar regions to southerly latitudes, and, as glaciers, descended from the summits of the mountain-chains into the plains.  Countless species of animals perished in this cataclysm of ice and snow, but man survived.

In his primitive savage condition, living for the most part on fruits, roots, shell-fish, man was in possession of a fact which was certain eventually to insure his civilization.  He knew how to make a fire.  In peat- beds, under the remains of trees that in those localities have long ago become extinct, his relics are still found, the implements that accompany him indicating a distinct chronological order.  Near the surface are those of bronze, lower down those of bone or horn, still lower those of polished stone, and beneath all those of chipped or rough stone.  The date of the origin of some of these beds cannot be estimated at less than forty or fifty thousand years.