« PrécédentContinuer »
I. The age of the Volcanic Throats of the Upper Karoo Formations of South Africa.-By Dr. John Shaw, F.G.S., F.L.S., Professor of Physical Science in the South African College.
[Read, 26th September, 1877.]
The surface contour of South Africa is not only of interest from a physical-geographical, but also from a geological point of view. It rises by terraces to an Upland Plateau which forms a belt-like tract, extending from the inland regions of the Colony, through the Free State, and into the Transvaal. There are three of these terraces, each bounded by a range of mountains. These ranges run more or less parallel to the coast. Geologically the coast belt of land is different from the first intramontane belt; that again from the second intramontane belt, which again is different from the Upland Plateau.
Taking a section from the Cape Flats and leaving out the Table Mountain mass as isolated (for such it must. be considered) from the main structural disposition of the country, we find that:-
From the coast to the first range there is clayslate of a Silurian Age with mountain tops of Lower Devonian, commonly known as the Table Mountain sandstone. This brings us to the Drakenstein mountains. The first intramontane tract is Upper Devonian and is bounded by the Bokkeveld. The second intramontane tract is of Carboniferous age and is the Lower Karoo bounded by the Roggeveld mountains. The Upland Plateau belongs to the Upper Karoo, its geological equivalent being considered the Triassic of the secondary epoch.
The Tertiary Formations are but poorly represented in South Africa, consisting merely of isolated patches, such as the Tygervley sandstone of the Cape Flats, shell beds at French Hoek, at the mouth of Sunday's River, the Oliphant River, the alluvial deposits of the Vaal River, &c.
TRANS. PHIL. SOC. 1877.-PART I.