THE HUMAN PERIOD. 585 



The chart explains itself. All the items occurring^ together in one 

 cdliiinii between two horizontal lines, represent the characteristics of 

 the period embraced by those lines. It has been found useful for de- 

 termining the relation in time of events originally referred to different 

 scales, and it also serves to divide the human period into smaller parts 

 than can any single scale. 



The chart relates to Europe only, the most thoroughly investigated 

 of the continents. Even so, its divisions are not contemporaneous for 

 all that land. The dawn of written history in Britain breaks eight or 

 nine centuries after that of Greece. The polished stone and the bronze 

 ages must have rolled over Europe in slowly moving waves. The ad- 

 vancement of the other arts and the domestication of animals similarly 

 spread from men to men, retarded by mountain chains and salty chan- 

 nels. But if these scales were applied to America, the later stone age 

 alone must be shifted downward at least five thousand years. 



