Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/158

 shales, sandstones, and calcareous grit contains the same forms of plants, as well as reptilian remains of Dicynodon, and lies conformably on a boulder-bed, which gives the impression that it was formed on the spot, and was not transported by the action of water. It is also remarkable, and an observed fact, that this boulder-bed of Southern India passes gradually into the succeeding shales and sandstones, which have been termed by the Indian geologists "the Ootatoor plant-beds." A lithologically similar boulder-formation I have also seen at the same horizon in the Cape Colony, passing beneath the blue Karoo shales ; and I am pretty certain that Mr. Bain and many of our African geologists have taken this boulder- bed, at many localities, for an igneous trappean rock. Mr. Bain (see his map) calls this boulder-bed, which dips under the " Ecca-beds " of the " Pataties Revier," " Claystone Porphyry." There is certainly a basaltic melaphyre, forming beds of considerable extent in this lowest part of the Karoo formation, as, for instance, can be seen near Platte-fontein, in the great Karoo; but this trap does not belong to the extensive beds of boulders at the base of the " Pataties Revier " shale. At first sight the trap and the boulder-bed have many similarities, as the material of the boulders is partly derived, from igneous rocks. Dr. Sutherland thinks that the boulder- bed was formed by glacial action, and tries to prove it by the observed fact of grooves and furrows on the plateaux of the Table- Mountain Sandstone. These grooves, quite similar to those in our Alps, occur in great abundance on the sandstone of the Ifumi river, about twenty miles south of Durban.

The greenstone (melaphyre ?) has found its way through this formation at many places, and forms beds between the strata of it. The greenstone contains a great quantity of pebbles of older rocks imbedded, which give it a speckled appearance. But it seems that the greenstone eruption happened at the earliest period of the forming of the Karoo beds, as the " kopjes " of greenstone are only found in the lowest strata of the " Pietermaritzburg shales," and in the succeeding sandstones. The series of greenstone " kopjes," which runs from the Ingeli Range in Kaffirland up through Richmond, York, and Greytown to the Tugela river, is of practical importance, as in it, or in the direction of its strike, the occurrence of copper ores can be traced through the whole of South Africa. Besides this Trappean greenstone, a second igneous formation may be found within the Karoo series, the so-called amygdaloid rock, which caps many of the heights of the upper Karoo beds, and often forms extensive beds between them. Prom it are derived the various kinds of chalcedony, agates, rock-crystals, and topazes which are so plentiful in the rivers of the Free States and Natal.

5. The Cretaceous Rocks of South Africa. — Between the rivers Umtamfuna and Umzambane, about five miles from the southern boundary-line of Natal, on the south-eastern coast of Africa, some deposits are found which at first sight seem to be of the same ma-