Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/47

 was not deep, and the whole Rush was soon dug out. These two facts give additional proofs in favour of the recentness of the deposits ; and consequently strong promise that the present river-bed may prove equally rich. The river Vaal is not a rapid stream. It flows sluggishly from one terrace to another, and falls in its course by a series of rapids at intervals of some miles. It winds about to a considerable extent throughout its entire progress. This is in favour of the view that the alluvial gravel has been deposited by the Vaal, as the country is one which the slightest elevation at particular points would alter so as to change the course of the stream for miles. The rapids are caused by basaltic dykes, which may be considered to be kopjes in the process of formation for a future time. Such dykes, moreover, are meanwhile " bars," and prevent the greater part of the material washed down from going beyond them.

The Isolated Diamond-fields are very different in soil from that of the Vaal River. The surface, instead of being a ferruginous loam, is in most cases calcareous. The pebbles are by no means many, and they are all angular and not water- worn.

I have visited the various isolated digging-spots. They are in geological and diamantiferous indications the same. The pebbly mass of the Vaal-River diggings glistens with beautiful agates and crystals of nearly every colour ; but the soil washed and sifted in the isolated diamond-fields is not by any means so attractive. The pebbles are fewer, occasional agates, crystals, abundance of tourmaline and garnet amid a mass of fragments of basalt and pieces of serpentine, all imbedded in a more or less calcareous soil, which glistens with talc and mica.

I had been, from the commencement of my study of the diamantiferous tracts of South Africa, on the look-out for the primary and metamorphic series.

I have mentioned the existence of granite in the trap-conglomerate of the Vaal ; and I got hold of a water-worn fragment of gneiss, which also occurs in the same conglomerate, as I afterwards discovered. I found, however, no decided traces of true metamorphic rocks till I examined the diamantiferous pans and isolated places. I collected in the course of one tour specimens of gneiss, chloritic schist, mica-schist, and talcose slate in different digging-spots. I found none of these rocks in situ ; and they no longer exist in connexion with the rock-system of the region, as far as I have been able to ascertain.

It is necessary, before going any further, to enlarge on the nature of these pans, the detritus drifted to which from surrounding tracts is now being searched for diamonds, and is found to contain fragments of the schistose series.

Du Toit's Pan is the most celebrated of all the diamantiferous pans, and may be taken as a type of the pans of the region.

I cannot indorse the views of Mr. Wyley in regard to the origin of the salts of these pans — that the saltness has been left to them by the sea, which at some period (he thinks comparatively recent) swept over the whole, or nearly the whole, of South Africa. With reference to his opinion that the land has been gradually elevated