Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/154

 to the overlying sandstone, to which it belongs, as I think, and not to the older clay-slate formation. It is remarkable that at the Tatin (so-called " goldflelds ") the slate formations have the same strike and are elevated at the same angle of about 70°. At the mouth of the Umzimculu, about seven or eight miles from it, and north of the young township of Murchison, the river breaks through crystalline limestone of enormous thickness, but whose position relative to the neighbouring strata is not clear. On both sides of the valley the limestone forms precipitous walls of some 1000- 2000 feet, which are luxuriantly covered with vegetation. Also the bottom of the river consists there of the same rock, the thickness of which towards the base is not known. On the surface it only covers a space of about four square miles.

3. Table- Mountain Sandstone. — The sandstone plateaux, which are so characteristic of the African landscape, lie perfectly horizontally upon the old slate formation, and at some places upon the granitic base. The sandstone, forming precipitous tableland, has never been disturbed ; nowhere is a folding of the deposits visible ; only fractures run through the zone, in which masses of Aphanitic Diorite are seen, which have burst through the granite and slate formation ; but nowhere is the sandstone raised up at an angle, or folded by the greenstone. The high plateaux are covered with a dense grass vegetation ; and numerous herds of cattle feed on the level summits of the tableland. The soil is extremely poor, and there is not even a shrub to interrupt the endless uniformity of the landscape. The rivers have made their way through the beds and strata of this sandstone, thus forming precipices, at some points several thousand feet in height. The sandstone shows the same lithological peculiarities as the Table-Mountain Sandstone of the Cape, after which it is named. The tops of many of the " table mountains " of the Colony are crowned by beds of a dark basaltic green- stone (fig. 1) which also possesses the same pillar-like structure as our basalt. It contains fragments of quartz, granite, and gneiss. In a variety of this igneous rock, from the " Great Karoo," I found small traces of gold. I never found any organic remains in the sandstone of the Colony itself, except in a thin soft shale, with much mica in it, which seems at the Krantzkop (fig. 1) to be a bed in the sandstone, from which I got some small bivalves and a finely striated Patella, both too indistinct for determination. Such shale is also exposed near the upper drift of the Omkomaz river, near Richmond, and at several other places in the Colony. The Sluten-Konga, Table Mountain near Pietermaritzburg, Inanda, and Noodsberg are examples of the regular-shaped table mountains of South Africa. The same shales and quartz-sandstone form the Krantzkop, which drops nearly vertically down to the Tugela river, about 3800 feet. The high plateau of it is capped with melaphyre-like greenstone. The basis of the Tugela valley is granite, intersected by dykes of an aphanitic diorite. The slate formation, the layers of which stand almost vertical, rests on the granite and is covered with the so-called " Doorns," the celebrated mimosa vegetation of South Africa : the great mass of the mountain is built up of sandstone, and crowned