PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 139 



same amount for the grinding action of the Gulf Stream, — 

 this would give us a period of about ten millions of years since 

 the termination of the cretaceous period. This estimate is pro- 

 bably far too high, judging by what we know of the wearing 

 action of water in hydraulic sluices ; we have a safer estimate 

 in a period of five millions of years as denoting the time which 

 has elapsed since the beginning of the tertiary. If we assume 

 with Ramsay that this represents about one tenth of the time 

 which may have elapsed since life appeared on the earth, we 

 should have a total of not more than fifty millions of years since 

 the first appearance of life upon this globe. To this must be 

 added, as indicating the age of the globe, whatever time mathe- 

 maticians think was necessary to reduce the globe from its 

 primitive state to a condition fit for animal life. 



