3 2 
THE TANGANYIKA PROBLEM. 
logical structure of the African interior, resulting from 
recent exploration, is particularly germane to the enquiry 
with which this work is concerned. 
Most, if not all, the existing views of the nature and past 
history of the African land-mass have been built upon the 
old conception that the physical characters of the con- 
tinent, the distribution of land and water upon its surface, 
the shape and the configuration of the equatorial region 
as a whole, have been almost unique in their stability 
and long permanence. That, in fact, the great mass 
of Africa, lay in waving hill, and plain, and ravine, 
much as it does now, even under the paleozoic sun ; 
or, at any rate, since the suns which rose over this 
portion of the earth, when the new red sandstone was 
being deposited, finally set. This conception of the past 
history of Africa was first definitely brought forward, 
now many years ago, by Sir Roderick Murchison* in a 
Presidential address to the Royal Geographical' Society, 
and it has ever since formed the chord upon which those 
who have concerned themselves with the geology of the 
continent have harped. It was, for example, resuscitated 
by Dr. Gregoryf while discussing Suess’ conception of 
the nature of the great Central African “ graben ” (rift 
valleys), and from this single instance, taken at random, 
it will be sufficiently obvious that, although we have until 
lately known almost nothing of the nature of the African 
interior, this ignorance, as usual, has in no way deterred 
investigators from speculating a good deal. What we 
require at the present time, and for the particular investi- 
gations upon which we are entering, is a review of the 
most recently ascertained facts touching the geology 
* Journal Royal Geographical Society, Vol. xxii. (1852) ; Ibid. Vol. xxviii. (1858). 
f The Great Rift Valley (1896). 
