1 64 THE MIGRATION GF BRITISH BIRDS 



species in, the summer and winter migrants to, and the 

 coasting migrants across that area, and to show the 

 proportionate avifauna of each of the three divisions of 

 the United Kingdom. Dealing then with the resident 

 species and each class of Migrant, we have endeavoured 

 to trace the sequence of their arrival in the British Area ; 

 and, finally, to append a tabic of the species and races 

 of birds that are peculiar to that area. The whole 

 subject is a most fascinating one, and full of promise ; 

 an un worked field to which I am afraid the somewhat 

 small limits of the present work have prevented me 

 from devoting a fuller measure of attention. Sufficient, 

 I hope, has been discussed to serve as a stimulus to 

 further inquiry. The new Law of Dispersal, by which I 

 have attempted to explain what up to the present time 

 have been universally regarded by naturalists as inex- 

 plicable phenomena, will, I trust, meet with some small 

 portion of tentative approval from biologists. 



As we remarked in our resume zX the close of Chapter 

 1 1., so we may again repeat here, that the Glacial Epoch 

 was the cause of extermination of the greater portion of 

 the fauna and flora of northern and temperate Euro- 

 Asia. Among this awful wreck of life we must un- 

 doubtedly include the Birds. Some of these species, 

 as v/c know from palaeontological evidence, must have 

 disappeared from the scene for ever ; others, the majority 

 of others, have left no trace behind them. Birds, it 

 ma\' be urged, could readily escape from such adverse 

 conditions: as the severe winters came on they could 

 retire south. But all the available evidence we can 

 biing to bear upon this question disproves the assump- 

 tion. In the Northern Hemisphere no bird increases 



