THE GLACIAL RANGE CONTRACTION, ETC. 83 



round the southern borders of the Sahara Sea or Desert, 

 and then northwards up the valley of the Nile, ultimately 

 following the more recently-formed coast-area of Tripoli, 

 as the sea receded, colonizing Algeria, and ultimately 

 spreading northwards into Iberia, into France, and 

 eventually the British Area. The line of Emigration 

 followed by those species in the past continues to be the 

 route of Migration in the present. A few individuals of 

 some of the species tabulated below may possibly win- 

 ter in Algeria and Tripoli, as, for instance, the Swallow, 

 but the great majority pass on to Tropical Africa, even 

 to West Africa and the Atlantic sea-board, by this 

 circuitous route ! It is a very significant fact that the 

 majority of these migrants are late to arrive at their 

 breeding grounds, as is customary with most if not all 

 species from the south-east. The only exceptions are 

 those of species the British individuals of which may 

 probably winter in Algeria — the three Swallows, and 

 the Yellow Wagtail. It is a still more significant and 

 suggestive fact — confirming the views above expressed 

 — that with the solitary exception of the Turtle Dove 

 not one of the species is common on migration at the 

 Canary Islands, as we should reasonably expect to be 

 the case did the birds journey north from Tropical 

 Africa by this route. Nay more, such common species 

 as the Yellow Wagtail, the Swift, the Goatsucker, and 

 the Garganey have never been noticed at the islands at 

 all ; whilst such wide-spread birds as the Cuckoo, the 

 Sand and House Martins, the Golden Oriole, and the 

 Spotted Flycatcher are only noted as stragglers to the 

 group. The Turtle Dove, however, is a very common 

 summer visitor to the Canaries, but there is no doubt 



