Richard Nathaniel Rubidge

“ The ranges of porphyry, like those of quartzite, die out and reappear. The normal position of the porphyry appears to be as in fig. 4, but I have seen it placed as in figs. 5 and 6:—
The character by which we all agree to recognize this rock is the presence of masses of quartz and granite of various sizes with occasional fragments of slate and other rocks. Sometimes these masses are as much as fifty pounds in weight, at others they are so minute as to be scarcely recognizable by the naked eye. ”

“ It is my conviction then (though I admit that my evidence is not quite conclusive) that the inclined slaty rocks of this Colony, west as well as east, all belong one formation, which geologists at home have, on the evidence of fossils, pronounced to be Devonian; and that the quartzite is a rock which has undergone a superficial change, and may therefore be called metamorphic. This siliceous metamorphosis is associated with other changes. The clay-slaty beds are often converted into ochry, micaceous, and chloritic schists. ”

“ These contain vegetable stems which have been recognized by many as identical with those of the Ecca. At Forester's Farm, east of Graham's Town, is a blue rock, just like that of the Ecca, containing the same fossils, which passes gradually into the gneiss. The sandstone on the one side is in relation on the other with the claystone-porphyry of Bain, as is the rock at the Ecca. Near Salem, in the heart of the Carboniferous system of Bain, are similar rocks with like fossils, conformable with the quartzite. ”

“ In Namaqualand the rocks between Springbok and Concordia were perhaps more decidedly gneiss-like than in any other part of the section, except perhaps near Kok Vontein, yet I regard these two spots (the former about a mile north of Springbok Vontein, the latter two miles south-east of Kok Vontein) as the main axial lines of the country. Many facts concur to prove that whatever may have been the cause of the upheaval of strata in this country, igneous rocks have had nothing to do with it. ”

“ There are few things I have more to regret in the way of lost opportunities than the want of a careful examination in detail of the country within ten miles' radius of the lowermost ford of the Olifant's river. It would include a section from the clay-slate to the Upper Silurian of Bain which are found in the Cederberg as well as the passage of the former into the felspathic rocks of Namaqualand. Bain has no hesitation in affirming this change, and I have every reason to think that he is correct ”

“ Still, it might be objected that there may really be a difference between the clay-slate and the Devonian, though Mr. Bain may have mistaken the line of division. If reference be made to the Admiralty chart of St. Francis Bay, it will be seen that the low shores of the bay are crossed by a range of mountains of considerable elevation. These mountains, which are quartzite, cross the strike at a considerable angle, nearly, in fact, for some distance at a right angle ”