Page:South African Geology - Schwarz - 1912.djvu/164

 Ecca, and the Umsikaba Beds are contemporary facies of one and the same series.

At the type section through this series at the Ecca Pass, near Grahamstown, the Upper Dwyka Shales are thoroughly calcined by the oxidation of the pyrites, the heat of the reaction and the consequent expansion having been sufficient to crumble the rocks into sharp folds, whereas the rocks on either side are unaffected. Above this white calcined rock there are brittle, thinly bedded shales breaking into angular slabs, and above this a bed of mottled purple sandstone (intermediate sandstone), and above this massive blue-black sandstone showing remarkably well the spheroidal weathering. This feature is usually exhibited in igneous rocks such as dolerite, and is due to contraction after consolidation. Above the massive sandstone there are brittle shales breaking into heaps of starch-like fragments, and on the very flat dip slopes there are exhibited roots and indeterminate stems of plants. All the shales are ripple-marked and sun-cracked, and show on a small scale a kind of spheroidal weathering, such as is often exhibited in mud that has dried after deposition. The mottling in white appears sporadically. Septaria also occur, the lime usually concentrating round centres of foreign bits of black shale in the sandstones.

The Ecca Beds on the south of the mountains are exposed against the Worcester-Swellendam fault at Worcester Station. They lie next to the Malmesbury Beds, so that the fault has a throw equivalent to —

Feet Part at least of the Ecca Beds 500 The whole of the Dwyka Series 500 The w hole of the Witteberg Series 1, 500 The whole of the Bokkeveld Series 2,500 The whole of the Table Mountain Series 5,000 And some portion of the Malmesbury Series 1,000 Total throw of the Worcester-Swellendam fault 11,000