RANGE BASE OR REFUGE AREAS 31 



period the Sahara was either a great eastern inlet of the 

 Atlantic, a relic of that vast primeval ocean which we 

 know swept from the Atlantic to the Bay of Bengal 

 during the Eocene and Miocene ages ; or a vast sterile 

 waste even more barren than at the present time, owing 

 to the more recent retreat of the sea. Whether the sea 

 actually invaded this area or not during Pleistocene 

 time is, however, of little consequence : the fact remains 

 that a vast barrier, either of sea or barren desert, 

 effectually prevented all northern progress in this 

 direction of plants and animals from Africa, and that 

 the southern range of all western and temperate 

 species never extended below this area. The vast 

 influence of the Sahara on the distribution of species 

 continues to be exerted down to the present time, 

 and the strictly Ethiopian fauna and flora have almost 

 entirely failed to establish any appreciable element 

 amongst the Palsarctic types that still continue to 

 occupy Africa north of that sterile barrier. In the 

 north-east of Africa, however, we find a very different 

 state of things, Ethiopian types ranging right up the 

 Nile valley to the shores of the Mediterranean. Owing 

 to the far easier conditions of dispersal we also find much 

 commingling of Palaearctic (more correctly described, 

 however, as of Ethiopian origin) and Ethiopian types 

 in this area, the former penetrating the Ethiopian region 

 to its southernmost limits, and from which region they 

 originally emigrated northwards, and the latter encroach- 

 ing upon the Palsearctic region to an appreciable extent. 

 The Ethiopian element persists throughout Egypt even 

 to the delta of the Nile ; and the range of between thirt\- 

 and forty species of birds characteristic of that region 



