Page:The journal of the Royal Geographic Society of London. Volume 34, 1864. (IA s572id13663720).pdf/416

202 year 1852, viz., that Central South Africa had, from the remotest secondary period, or that of the fossil reptile Dicynodon, maintained its undisturbed lacustrine and terrestrial characters up to our own days. I suggested, in short, that what Africa was when the Dicynodon lived would be found to be true in the present day, by our finding a series of lakes and marshes in the centre of the country, the waters of which, occupying plateaux, escaped through fissures in flanking and higher coast ranges of older rocks. I have in subsequent addresses reverted to this view as confirmed by advancing discoveries.

Livingstone demonstrated the truth of this theory as regarded the Zambesi, and it-has been well sustained in other regions (particularly in Central Equatorial Africa), by the researches of Burton, Speke, and Grant.

The point to which I specially wish to direct the attention of the Society at present is, that in none of these adventurous journeys in the interior have the travellers met with marine fossiliferous formations, which would indicate that this continent had been submerged, like most other countries, during the secondary, tertiary, or modern periods. Nowhere have they detected limestone with marine organic remains, though I specially urged both Livingstone and Speke in their last journeys to endeavour to discover such rocks. The late lamented Mr. Richard Thornton, the accomplished young geologist who accompanied Livingstone, was moreover particularly charged to look keenly for such reliquiæ, and with all his zeal he found fossil land plants of the carboniferous era only.

The only marine shells which have been detected, occur on or near the coasts. Some of these are of Eocene nummulitic age, and others, as at Natal, indicate a very recent elevation of shore deposits. In a letter to myself, Mr. Thornton describes these tertiary rocks as occupying a coast ridge rising to 200 and 300 feet above the sea on the mainland opposite to Zanzibar, from observations which he made when he accompanied Baron von der Decken to Kilima-njaro.

Let it, however, be clearly understood that my view of South Africa applies to the great interior only. For, geologists have long been aware that the Cape Colony has an external fringe of hard ancient marine deposits of palæozoic age, associated with rocks of igneous origin.

That there exists a framework of old rocks is manifest indeed from the excellent geological map of the Cape Colony, by Mr.