124 GEOLOGY AND HISTORY 



need not necessarily have suggested themselves to 

 the mind in such a connection.' l 



On the geological side, the following may be 

 accepted as a summary of facts : 2 



' 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 pleistocene or glacial period, or in 

 what has been called the " continental " period of the 

 post-glacial age, because the new lands then raised 

 out of the sea exceeded in extent those which we 

 now have. We have some measures of the date of 

 this great continental elevation. Many years ago, 

 Sir Charles Lyell used the recession of the Falls of 

 Niagara as a chronometer, estimating their cutting 

 power as equal to one foot per annum. He calcu- 

 lated the beginning of the process, which dates from 

 the post-glacial elevation, to be about thirty thousand 

 years ago. More recent surveys have shown that the 

 rate is three times as great as that estimated by 

 Lyell, and also that a considerable part of the gorge 

 was merely cleaned out by the river since the pleis- 

 tocene age. In this way the age of the Niagara 

 gorge becomes reduced to perhaps seven or eight 

 thousand years. Other indications of similar bearing 



1 Les Origines de FHistoire. Brown's translation. 



* Modern Science in Bible Lands, 1888, pp. 244, 245, 251, 252. 



