THE GLACIAL RANGE CONTRACTION, ETC. 8i 



The species marked A in the above table winter, or 

 winter and breed, in Iberia or North-west Africa, or 

 both, but only winter in or pass through South-east 

 Europe, Asia Minor, Palestine, and North-east Africa 

 on passage to regions further south to spend the cold 

 season, extending in some cases even to the Cape Colony. 

 This circumstance appears to me to prove two facts. 

 First, that the ancient Sahara Sea barred further pro- 

 gress to the south in the western portions of Africa, as it 

 had previously barred northern progress say in Pliocene 

 ages ; and second, that North-west Africa and Iberia 

 formed the glacial Refuge Area or Range Base of the 

 British or West European portion of those species ; 

 the individuals breeding further north in the eastern 

 portions of the continent than in the western portions, 

 perhaps, during Pre-Glacial ages, and even continuing 

 to do so during the progress of the Glacial Epoch, as 

 we have already seen the extension southwards of the 

 ice-sheets in the east was much less than in the west 

 {conf. p. 28), thus leaving a wider expanse of breeding 

 area northwards during the successive cold periods. 

 By applying the well-established Law of Migration, 



that the birds that breed the furthest north winter the 



G 



