228 VIGNETTES FROM NATURE. 



occupy the deserted plains of temperate Asia 

 and America. 



In the eastern hemisphere, however, the 

 conditions have been unfavourable to their 

 rapid northward progress. In Asia, the great 

 central region is occupied by the snowy 

 mountain ranges of the Himalayas and the 

 Hindu Kush, and by the high table-land of 

 Thibet, which cut off the cold Siberian plains 

 from the rich fauna and flora of the Indian 

 region ; in Europe, the Mediterranean and 

 the Caucasus similarly divide us from Africa, 

 which is itself cut almost in two, biologically 

 speaking, by the practically lifeless district of 

 Sahara. Hence it is only in America that 

 the fauna and flora have been free to make 

 their way back unimpeded from Carolina and 

 Georgia to New England and the St. 

 Lawrence basin. Even here, the re-peopling 

 has been far from complete ; while in isolated 

 portions of Europe, like Great Britain, and 

 still more markedly Ireland, where the fauna 

 and flora had hardly time to penetrate before 



