SUMMARY OF RESULTS 215 



two or three thousand years before the Deluge of 

 Noah, while some estimates of the antiquity of man, 

 based on physical changes or ancient history, or on 

 philology, greatly exceed this limit. If the earliest 

 men were those of the river gravels and caves, men 

 of the ' mammoth age,' or of the * palaeolithic ' or 

 palaeocosmic period, we can form some definite ideas 

 as to their possible antiquity. They colonised the 

 continents immediately after the elevation of the land 

 from the great subsidence which closed the pleisto- 

 cene or glacial period, in what has been called the 

 1 continental ' period of the post-glacial age, because 

 the new lands then raised out of the sea exceeded in 

 extent those which we have now. We have, as 

 stated in a previous chapter, some measures of the 

 date of this great continental elevation, and know 

 that its distance from our time must fall within about 

 eight thousand years. Many indications, both in 

 Europe and America, lead to the belief that it is 

 physically impossible that man could have colonised 

 the northern hemisphere at an earlier date than this 

 geologically recent continental period. 



6. There is but one species of man, though many 

 races and varieties ; and these races or varieties seem 

 to have developed themselves at a very early time 

 and have shown a remarkable fixity in their later 

 history. There is reason to believe, however, from 

 various physiological facts, that this is a very general 

 law of varietal forms, v/hich are observed to appear 

 rapidly or suddenly, and then in favourable circum- 



