222 A NATURALIST IN MID-AFRICA. 



If we take the period when natural orders and 

 the leading genera of plants were pretty well diffe- 

 rentiated, and if at that time we assume a sea in 

 place of the Sahara stretching across the whole 

 desert country which now extends from Belu- 

 chistan to the Atlantic, between Morocco and 

 Senegal, an explanation can be given. There 

 would, of course, be islands in this sea, but the 

 most important point is that the range of moun- 

 tains about the Eed Sea, with those of Abyssinia, 

 would form a climatic bridge to the ancestors 

 of the Mediterranean flora ; hence there would 

 be no difficulty in understanding the distribution 

 and affinities of the Alpine flora of Africa — (high 

 level, wet and cold-loving plants) which probably 

 came across at that time. At this period the 

 ancestors of the low-level steppe flora may have 

 covered the whole of the continent south of 15 

 degrees N. latitude. 



Along the southern shore of the Sahara sea 

 would be a continuity from the coast of the Indian 

 Ocean to Timbuctoo ; at this time neither the 

 Niger, Congo, or Nile would have excavated their 

 basins, but all Africa south of 15 degrees N. lati- 

 tude might have been fairly high ground. 



Now, under these circumstances, first, the Coast 

 .Jungle Flora of India and Malaya, as it existed at 

 Unit (late, would colonise the southern shore of the 

 Sahara sea. 



Now, if we imagine the rivers beginning their 



