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. 
