INTRODUCTION 



" rills." If all the air and water were removed from the earth, 

 then the Rift Valley would present much the same aspect to 

 an inhabitaiU of the moon as some of the larger of the lunar 

 rills present to us. So the exploration of the Rift Valley has 

 the additional attraction of offering the possibility of explaining 

 the nature of some features in the surface of the moon. 



We are now fairly acquainted with the rough outlines of 

 the geography of most of the line of the great African " rill." 

 Our knowledge, however, of the geological structure of its 



Fig. 2. — Rift Valleys of the Moon. Part of the Moon, including Mercator, etc. 

 (From Nasmyth.) 



African course is very imperfect, while one part of it in 1892 

 had not even been reached by Europeans. This was greatly 

 to be regretted, because its study might be expected to 

 yield much important evidence. The desire to obtain more 

 precise geological information as to the structure of this 

 Rift Valley was, therefore, the main reason for the journey 

 described in this volume. Before proceeding to the narrative, 

 however, it is advisable briefly to refer to the history of the 

 exploration of the region of British East Africa, in which the 

 route of the expedition lay. 



