350 ALTERNATE GLACIAL PERIODS. Cuap. XI. 



New Zealand, niio^'ht have become slightly tinted by the same 

 peculiar forms of life. 



Sir C. Lycll in a striking' passage has speculated, in lan- 

 guage almost identical Avith mine, on the effects of great alter- 

 nations of climate throughout the world on geographical dis- 

 tribution. And we have uow seen that Mr. Oroll's conclusion, 

 that successive Glacial periods in the one hemisphere coin- 

 cided with warmer periods in the opposite hemisphere, to- 

 gether with the admission of the 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 certain periods from the 

 north and afterward 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 Hving 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 com- 

 pared with savage races of man, driven up and surviving in 

 the mountain-fastnesses of almost every land, Avhich serve as a 

 record, full of interest to us, of the former inhabitants of the 

 surroundinjr lowlands. 



