Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/32

 seems evident that the diamantiferous deposits of the Vaal are not the result of any single or abrupt operation of nature, as some have suggested, either in the shape of some " great debacle," or volcanic eruption, but rather that, for some enormous period of time, there were long-continued causes at work, occasioning a distinct sequence in the different wide-spread accumulations of boulder-drift, clays, and gravels of which they are composed.

At Hebron and Diamondia this is clearly the case : there we find, first, the unstratified cemented gravel and boulders, as shown at d, in fig. 2 ; the terrace-like deposits at c, c, were deposited probably at the close of the same period. Then followed the boulders and gravelly clays, marked Nos. 1, 2, 3, 5, 6, and 7. All these in their turn have undergone great denudation, the lateral drainage from the more level country having divided them into separate terrace- like mounds and isolated kopjes, the intermediate portions having been carried away, and a rearrangement of portions of the gravels {e, f, and g) having taken place at a lower level in the ancient trough of the old rocks b, b. These latter gravels are much more sandy than the more ancient drifts, large portions of their clayey elements having necessarily been washed out of them during the period of readjustment. Finally, this last deposit (e, f, and g) has been cut through by the river in forming its present channel.

The question now arises. Were the more ancient boulder-gravels derived from a local source, or have they travelled from a distance ? And, if so, what is the probable direction whence they came ? and by what agency were they transported to the localities where they now are ?

Although the original locality of the true matrix of the diamonds found in them has not been discovered, still there can be little doubt that a large portion of the constituents of these deposits has come from great distances.

At this point, the tell-tale fragments of fossil wood, worn and polished as they are, become most interesting and valuable evidence. Zones of fossil wood extend almost the entire length of the Stormberg* ; and magnificent specimens are found in many places on the northern side of these mountains. I have been told, by the Hon. Theophilus Shepstone, that, in his journeys through Kaffirland, he has traced the existence of large quantities of fossil wood along the Quathlamba or Draakensberg range to Natal. I am not aware, however, that these zones have been found stretching to any great distance northward, or in a north-westerly direction from these ranges, towards that part of the diamond-bearing fields now under consideration.

Place of Origin of the Drifts. — It was always believed in the Cape Colony that the country rose towards the far interior in a succession of steps ; but the results of Mr. Graham's barometrical observations show this to be, to a certain extent, incorrect. From the coast to the ridge of the Stormberg, however, it holds good, and along a line within a certain distance of the western face of these mountains :


 * Quart. Journ. GeoL Soc. vol. xxvii. p. 523 &c.— T. R. J.