It is hardly contended that the neolithic age could have been more than four or five thousand years ago.  There is always the greatest difficulty in fixing any dates because from the nature of the case written records are absent, and the stages of growth in the history of peoples overlap so.

We know that sharp flakes of stone were still used for knives in the time of Moses and Joshua.  We are not out of the stone age yet, as regards some portions of the globe; and it is quite possible that parts of the earth, not so very remote, may have been still in the midst of a stone age when Assyria, Chaldaea, and Egypt were comparatively highly civilized.

It is also fairly certain that between the neolithic or smooth-stone age, and the palaeolithic, certain important geological changes took place, though those changes were not such as to have demanded any very great length of time for their accomplishment.

The palaeolithic stone implements are found in river gravels and clays, along the higher levels of our own Thames Valley, that of the Somme in France, and in other places.  They are also found at the bottom of various natural caverns.

No human bones have been found as yet with the implements, but the bones of large numbers of animals have.  And it seems certain that the men who made the implements were contemporaries of the animals, because in the later part of the age, at any rate, they drew or scratched likenesses of the animals on bone.  Among these representations are figures of the mammoth an extinct form well known to the reader by description and museum specimens of remains.

The animals contemporary with these primeval men were the mammoth, species of rhinoceros and hippopotamus, the “sabre-toothed” lion, the cave-bear, the reindeer, besides oxen, horses, and other still surviving forms.

In his address to the British Association in 1881 Sir John Lubbock called attention to the fact that these animals appear to indicate both a hot and a cold climate, and he referred to the fact (known to astronomers) that the earth passes through periods of slow change in the eccentricity of its orbit, and in the obliquity of the ecliptic.  The result of the latter condition is, to produce periods of about 21,000 years each, during one-half of which the Northern hemisphere will be hotter, and in the other the Southern.  At present we are in the former phase.

But the obliquity of the ecliptic does not act alone; the eccentricity of the orbit produces another effect, namely, that when it is at a minimum the difference between the temperatures of the two hemispheres is small, and as the eccentricity increases, so does the difference.  At the present time the eccentricity is represented by the fraction .016.  But about 300,000 years ago the eccentricity would have been as great as .26 to .57.  The result, it is explained, would have been not a uniform heat or cold, but extremes of both; there would probably have been short but very hot summers, and long and intensely cold winters.