CHAP. X 1 1 PLA TEA U ER UP TIONS 2 1 5 



uncouth lizards, the Siberian tundras of buried mammoths, and 

 the Weald of Kent of bird-like saurians. The lake deposits of 

 Equatorial Africa might have been expected to be especially 

 prolific in extinct animals, for the existing fauna is much 

 richer than those of the regions enumerated. Nevertheless, so 

 far they have proved barren. The conclusion has therefore 

 been gradually accepted that Tropical Africa is geologically 

 uninteresting, for as a continent it has no history, and it has 

 no message as to the development of life on the globe. 



A quotation in the Introduction (p. 2) shows that the 

 old view of the simplicity of the geology of Tropical Africa 

 has lasted as late as 1891, but in the next year Professor 

 Suess's memoir threw a special interest over the region adjoining 

 the Great Rift Valley. This, however, did not contradict 

 Murchison's brilliant guess as to the antiquity of the continent, 

 and I was not surprised when the four months on the coast- 

 lands and the first month of the march inland showed nothing 

 of any special geological interest. But nearer the Rift Valley 

 the conditions are different, and the region presents a combina- 

 tion of features which elsewhere can be paralleled only, and 

 that imperfectly, in the Western States of America. 



Plateau Eruptions. — The first of these special types of 

 structures was seen the day after leaving Machakos, when we 

 reached a tract of country marked on the best existing geo- 

 logical sketch-map as recent alluvium. It was part of the 

 district known as the Kapte Plains, and I expected to find 

 this to be an old lake basin or a desert of wind-borne drift. 

 But on reaching the summit of the last ridge of the Iveti 

 Mountains, we found before us a vast expanse of undulating 

 prairie, stretching away to the western horizon. The rock of 

 which this consisted ended abruptly against the flank of the 

 old gneiss ridge on its margin, but it ran up the valleys and 

 into the hollows of the mountains, just as the water of a lake 

 follows the irregularities of its shore. So much did this view 

 remind me of that across the great Snake River lava fields of 

 Idaho, when seen from the range of the Tetons, that I felt sure at 

 once that this was a plain of lava and not of alluvium. I hastened 

 down to it, and the inference was confirmed. The resemblance 

 between this plain and the American lava sheet became still 

 more apparent as we marched across it, and also when, on the 



