Notes on Ancient Boulder-clay of Natal

Abstract

T here is largely developed in the Colony of Natal a formation which seems to be in all essential particulars identical with Mr. Bain’s claystone porphyry of the Cape of Good Hope. This formation flanks a long range of sandstone hills, which runs from the Tugela river frontier, at a distance of some six or eight miles from the sea, across the Umgeni river, and through the Berea hills to the mouth of the Umbilo. It also crops out extensively near Maritzburg, and stretches thence, in one direction, over the Umgeni and Umvoti to the Tugela valley between Greytown and the Biggersberg; and in the other direction over the Umlasi and Umkomasi towards the opposite frontier. In the latter course it goes onwards to the St. John’s river and to the further districts of the Cape. The deposit itself consists of a greyish-blue argillaceous matrix, containing fragments of granite, gneiss, graphite, quartzite, greenstone, and clay-slate. These imbedded fragments are of various size, from the minute dimensions of sand-grains, up to vast blocks measuring 6 feet across, and weighing from 5 to 10 tons. They are smoothed, as if they had been subject to a certain amount of attrition in a muddy sediment; but they are not rounded like boulders that have been subjected to sea-breakers. The fracture of the rock is not conchoidal, and there is manifest in its substance a rude disposition towards wavy stratification. The general appearance is that of a clay which has been deposited by aqueous action