1 62 THE MIGRATION OF BRITISH BIRDS 



long past ages followed this route to the Arctic 

 regions. 



In the beginning of the present chapter we have 

 discussed the possibility of undiscovered breeding 

 grounds between Greenland and Spitzbergen of several 

 northern birds, as an explanation of various apparent 

 anomalies of distribution ; and by an analysis of the 

 table containing the species that emigrated in a north- 

 westerly direction to Iceland and Greenland, we have 

 shown what a great and significant proportion of 

 species continue to breed along the entire route from 

 the British Area to Greenland, and a still greater pro- 

 portion between Iceland and our area. We have also 

 shown that in two cases at least the highest northern 

 emigration of the species throughout the world has been 

 along this route. We next proceed to discuss the two 

 dominant lines of Post-Glacial Emigration in West 

 Europe, illustrating by a table the range extension 

 northwards of 206 species, and their relation to the 

 British avifauna. By means of this inquiry we discover 

 the astonishing fact that a vast percentage of species 

 range absolutely higher on the Continent than they do 

 in our area, notwithstanding its much milder climatal 

 conditions — a discrepancy of distribution due entirely to 

 the dominant line of Emigration followed in past ages, 

 and a fact which proves that the individuals of certain 

 species breeding in North-west Europe (say in Scandi- 

 navia) are descendants of the individuals tliat dwelt in 

 the south-east (Refuge Area III.) ; whilst individuals of 

 the same species breeding in cur islands, and as far 

 north as Holland or Dcnmarlc, are the descendants of 

 other individuals that dwelt in the south (Refuge Area 



