Mr. J. E. S. Moore's interesting work on the “Tanganyika Problem,” reviewed on p. 418 of the September number of the Geological Magazine, raises some interesting points in connection with African geology, though, as your reviewer rightly remarks, we are indebted to Mr. Moore rather for a statement of the problem “than for proposing an adequate solution of it.” At the same time it must be admitted that Mr. Moore's general geological conclusions appear to me, as a worker in Africa, much more in accordance with the facts as I see them in the course of my every-day life, than the hypotheses of certain eminent geologists who have preceded him. There is always a great disposition on the part of visitors to a little-known country to theorise, without having had time or opportunity for making those accurate and detailed observations which are essential if deductions are to be made which will stand the test of time. And the worst of it is, ‘authority’ has so much weight that local workers have the utmost difficulty in removing false impressions which may thus be caused. Two points to which I may refer are the “antiquity of the African continent” and the so-called ‘Rift-valleys.’ Now whatever may be the antiquity of Africa as a land surface, facts are constantly coming to light which throw great doubt on its having the stability attributed to it. Fossils of Jurassic and Cretaceous age are known from numerous places, and though these are chiefly confined to the coastal fringe, fresh discoveries are frequently increasing the area, such as the recent one far inland in the Sahara.