228 THE ETHIOPIAN REGION. [CHAP. 



Cancer ; northern Africa, as it did in the Pliocene, clearly forming 

 a part of the Holarctic region. The greater part of 

 the Sahara, as well as the northern portion of 

 the Nubian desert, although included in the Holarctic, will form 

 a kind of transition zone towards that region, as is also the case 

 with Syria, where a considerable number of Ethiopian types of 

 mammals are met with, while western Arabia shows a decided 

 approximation to the Oriental region, as is well exemplified by 

 the occurrence there of a species of the short-horned goats con- 

 stituting the genus Hemitragus. As has been stated in an earlier 

 chapter, the Sahara and Nubian deserts, although they have 

 apparently never been submerged since the Cretaceous epoch, seem 

 always to have formed a more or less complete barrier to the passage 

 of the mammals of Algeria and the adjacent countries into the 

 Ethiopian region ; and the main migration from the north and east 

 has thus taken place along the north-eastern side of the continent. 

 With the exception of its southern extremity, the whole of this 

 vast area lies within the tropics. As regards its physical features, 

 Dr Heilprin writes that " it presents several well-marked physical 

 peculiarities. In the first place, we have the vast expanse of 

 desert, which in the north occupies a transverse band varying in 

 width from about four to nearly ten degrees of latitude. This is 

 succeeded by what may not improperly be termed the open 

 pasture-lands, which as a narrow belt bounds the Sahara on the 

 south, curves southwards at about the position of Kordofan, and 

 occupies the greater portion of the continent lying east of the 

 thirtieth parallel of east longitude and south of the fifth parallel of 

 south latitude. A very considerable portion of this pasture-tract 

 forms a plateau of from four thousand to five thousand feet eleva- 

 tion. Included within it, and bounded on the west by the Atlantic 

 Ocean, is the region of the great equatorial forests, to the present 

 day a terra incognita in great part both to geographers and 

 naturalists. That portion of the African continent lying south of the 

 tropic of Capricorn differs in many respects, both as to its physical 

 configuration and its vegetable products, from the region to the 

 northward, and is characterised by a vegetation which is one of 

 the richest and most remarkable on the globe. With this marked 

 peculiarity in its vegetable development there is of necessity a 



