With so many new discoveries in hand Livingstone had an opportunity for working out several problems, and instituting comparisons between the phenomena of Inner Africa and the well-marked changes which go on in other parts of the world.

We find him at this time summing them up as follows:--] The subject of change of climate from alteration of level has not received the investigation it deserves.

Mr.Darwin saw reason to believe that very great alterations of altitude, and of course of climate, had taken place in South America and the islands of the Pacific; the level of a country above the sea I believe he thought to be as variable as the winds.

A very great alteration of altitude has also taken place in Africa; this is apparent on the sea-coast of Angola, and all through the centre of the country, where large rivers which once flowed southwards and westwards are no longer able to run in these directions: the general desiccation of the country, as seen in the beds of large rivers and of enormous lakes, tells the same tale.

Portions of the east coast have sunk, others have risen, even in the Historic Period.