Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/43

1871.] Pebble of peculiar Agate-breccia, with ancient fracture.

Subangular Agate, various ; and fresh fragments of Agate.

Subangular piece of Magnetite.

No. 26. From the T'somo, No. 2. Page 14.

Coarse grey Quartz-grit, weathering brownish, with disseminated Mundic (small cubes). Hard coarse Clay-schist, with disseminated Mundic. Small fragment of calcareous vein-stone with Copper-pyrites; small fragment of quartz-vein with Copper-pyrites; a morsel of quartz-vein with Iron-pyrites; and a small piece of tine-grained Galena.

No. 27. From the T'somo, No. 1. Page 14.

Hæmatite with quartz.

have presented in the various parts worked for diamonds up to the present date two apparently different classes of soil in which diamonds are found imbedded. The one class exists along the Vaal Biver and its tributaries, the Reit and Hart Ravers; and the other occurs in the Orange-River Pepublic, in isolated spots, generally circumscribed, and in many cases in what are called "Pans," which are basin-like hollows, in wet seasons more or less filled with water of a saline character, in dry seasons presenting a whitish surface saturated with salts.

I shall endeavour to show that there is really no distinction in the geological origin of the two classes. It will be convenient, however, in the first place to treat them separately, for the sake of clearness.

The prevailing rocks of the Vaal region and the isolated diamond-farms are trappean—greenstone and basalt. There is every indication that the upheaval of these has been continued throughout a vast length of time, and has extended until recently, geologically speaking. The summits of the hills consist of trap, which has been protruded through vast layers of sedimentary strata—generally calcareous sandstones, clay-slate, and such like rocks, all remarkably barren of fossils. Yery little disturbance is shown in the lie of these sedimentary rocks. Hence the prevailing character of the ranges is tabular, though dome-like, conical, and even pointed peaks are seen. They are dispersed more or less circularly around dreary flats, which are in many instances of considerable extent. The trap,