!I4 
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 1 1 1, 
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 
