Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/713

 noticed, the closing up of these openings would turn large portions of the present flats into wide lakes), there are no traces of more recent lacustrine deposits that I know of ; so that, with the exception of the unstratified clays and boulder-clays, and a little alluvial soil, nothing is found, in this portion of the area, of later date than the present drainage-system. This has, no doubt, tended in a great measure to prevent a spontaneous renewal of timber-growth after the extinction of the ancient forests (see p. 538), the soil having never been renovated by new deposits formed beneath the ocean, as it has in other countries. It must also be more difficult for the seeds of trees and plants to ascend to an elevated plateau than to spread over plains on a lower level, or just emerging from the waters.

Conclusion. — The foregoing collection of facts must, I think, tend to prove that vast climatal changes have taken place during the deposition of the various formations that have been brought under review in this and the foregoing portions of my paper. It may be objected that, with regard to such an extreme climate as is here inferred, South Africa is too far removed from the present Antarctic regions, and that the causes of great changes of climate are not understood.

The simple oscillation of the poles, however, taken together with the continual and necessary alteration in the distribution of land and water, would be surely sufficient to account for all the phenomena yet known, changing not only the geographical configuration of the surface of the earth itself, but carrying with it the most important changes of climate over every portion of the earth.

In such a case, when the London area possessed a tropical climate, the spot now occupied by Algoa Bay would be at some 68° south latitude ; or when the site of modern London was within or near the Arctic circle, Algoa Bay would be within 5° or 6° of the equator, with a temperature congenial to the existence of the large Venericardia of the Zwartkops Pliocene limestone (p, 534), In the former case, South Africa would then possess (instead of mountains covered, as at present, with snow for a few days in winter) an Antarctic cold, with an ice-bound coast, and glaciers covering every portion of the country.

Lastly, I have to notice in connexion with the geology of South Africa the rare occurrence of the remains of either fish or mammals. What has opposed their preservation? And further, was South Africa the home of large Pachydermata during a period equivalent to the Mammoth age ?

Until within a very few years, the rivers of South Africa swarmed with Hippopotami ; and large herds of Elephants roamed over the wide plains, which were also the home of the Giraffe and the Rhinoceros, and where the large Carnivora, Leopard, Panther, and Lion, preyed upon the weaker animals. Are we, then, to find, in our Pliocene deposits, Ostriches of gigantic size, enormous Lions, and Elephants eclipsing the Mammoth itself — analogues of the great Marsupials of Australia, the Mylodon, Megatherium, and Glyptodon of South America, the Mastodon and Mammoth of the Northern

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