ii 4 THE TANGANYIKA PROBLEM. 



crossed diagonally until I reached the lake itself. On this 

 series of marches we passed off the mountain slopes on to 

 plains of alluvium and old lake deposit in which there are 

 the remains of fresh-water shells similar to those which still 

 live in the lake ; and from this, it is obvious that the lake 

 once extended over these regions which are now covered 

 with thick forest of different sorts. As we neared the lake 

 we passed out of the forests, first into park-lands and then 

 over steppes with only a very few trees, and finally on to 

 the absolutely treeless salt wastes bordering the shores of 

 the Albert Nyanza. We were travelling over the old lake 

 deposits all the way, and the shelly remains became fresher 

 and fresher until we actually reached the shores of the lake 

 itself. Moreover, on the western shores of the lake we 

 found old water marks and beaches which show, in as con- 

 clusive a manner as similar terraces on the west coast of the 

 Albert Edward Nyanza, that the lake has steadily fallen 

 and receded to the north during a number, but an unknown 

 number, of years. From this it will be obvious that in our 

 marches from the Mountains of the Moon to the shores of 

 the Albert Nyanza, we were passing over land which had 

 been covered with water at a more and more recent date, 

 and conversely, as we returned over the road we had come, 

 we were passing over land which had been land for a longer 

 and longer time owing to the gradual northern recession of 

 the lake ; and the different age of the land was related to a 

 different type of flora which was growing on it. This differ- 

 ence in the character of the vegetation encountered during 

 the journey has been represented in the figure on page in, 

 which is a combination in sequence of a number of 

 drawings and photographs I obtained of the kinds of 

 vegetation through which we passed. By the lake shore 

 there was a belt of reeds, and beyond this, almost desert 



