II.—The Tygerberg Anticline

Abstract

Round the south-western corner of Cape Colony there is a belt of mountains which exhibit a number of exceedingly interesting features. The ranges meet almost in a right angle, the one set trending north and the other east, from a point near Ceres village; this is what Suess calls a ‘Schaarung,’ and I believe nowhere else in the world does this structure show itself in such a simple manner. Each range is composed essentially of an S-shaped bend, the syncline on the coast side and the anticline on the inner side, while subsidiary folds are added in various places, without, however, obscuring the general nature of the mountain structure. The central axes of the ranges are composed ofa coarse grey false-bedded sandstone, the Table Mountain Sandstone resting on the outer side on Pal-Afric beds, slates, phyllites, and intrusive granite, and dipping under later and conformable beds on the inner sides. The age of the Table Mountain Sandstone is uncertain, as, with the exception of indeterminable bivalves found by Griesbach in Natal and possibly a Patella, no fossils have been recorded from the series; the overlying beds, however, the Bokkeveld Beds, contain a rich fauna belonging to the American type of Devonian species. On top of the Devonian conies another series of sandstones, the Witteberg Beds, strongly differentiated from the older sandstone series by their yellow and red tints, and the amount of shaly matter intercalated between the sandstone banks.The Witteberg Beds, although strictly conformable to the Bokkeveld Beds, contain a flora which is referable to the Lower Carboniferous, the conformity being supposed to be the result of the ocean floor, during the period occupied elsewhere with the deposition of the Middle and Upper Devonian, having sunk below the area, or rather out of reach of deposition of land detritus.