THE TANGANYIKA PROBLEM. 
53 
generally been produced by the formation of heights and 
valleys due to lateral pressure, and consequently the 
crushing down of their floors (which as we saw in the 
region of Nyassa is actually taking place at the present 
time) must have produced tremendous heat, while the 
tendency for water to accumulate in these depressions will 
have led naturally to the production of volcanic phenomena 
along the hollow courses of the folds. 
