26 GEOLOGY AND HISTORY 



vicissitudes of this reign of ice, but there can be no 

 doubt that it destroyed much of the animal and 

 vegetable life of the pliocene, or obliged it to migrate 

 to the southward. In this period great deposits of 

 mud, sand and gravel were laid down, which prepared 

 the world for a new departure in the succeeding age. 

 This we may name the post-glacial, or early modern 

 period, and in it we have the most certain evidence 

 of the existence of man, though the geographical 

 arrangement of our continents and their animal in- 

 habitants were in many respects different from what 

 they now are. If geologists are right in the conclu- 

 sion already stated, that the close of the glacial 

 period is as recent as 7,000 years ago, this will give 

 us a narrow limit in time for the age of man, at 

 least under his present conditions. 



While, however, there is an absolute consensus 

 of opinion among geologists as to the existence of 

 man at or about the close of the glacial age, in 

 the northern temperate regions at least, there are 

 some facts which have been supposed to indicate a 

 pre-glacial human period, or the advent of man even 

 as early as the middle of the cenozoic time. These 

 merit a short consideration. 



