350 THE ORIGIN OF SPECIES 



slow modification of species, explains a multitude of facts in the 

 distribution of the same and of the allied forms of life in all parts 

 of the globe. The living waters have flowed during one period from 

 the north and during another from the south, and in both cases 

 have reached the equator; but the stream of life has flowed with 

 greater force from the north than in the opposite direction, and 

 has consequently more freely inundated the south. As the tide 

 leaves its drift in horizontal lines, rising higher on the shores 

 where the tide rises highest, so have the living waters left their 

 living drift on our mountain summits, in a line gently rising from 

 the arctic lowlands to a great altitude under the equator. The 

 various beings thus left stranded may be compared with savage 

 races of man, driven up and surviving in the mountain fastnesses 

 of almost every land, which serves as a record, full of interest to 

 us, of the former inhabitants of the surrounding lowlands. 



