Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/35

 along the present river-valleys, in the unstratified gravels and other deposits described above. On the other hand, how near these rocks approach the diamond-deposits on the northern side, and what may be the exact position of the original matrix from which the diamonds were really derived, have yet to be determined.

Dr. Voysey, Geologist to the Trigonometrical Survey in Southern India, has stated " that the matrix of the diamonds produced in Southern India is the sandstone breccia of the clayslate formation." As some of the formations in India are closely allied to those of Southern Africa, it would be interesting to ascertain whether any rocks similar to those mentioned by Dr. Voysey are to be found either in the extensive range of the Quathlamba, or in any of its offshoots.

The same authority further states " that the diamonds found in the alluvial soil are derived from the debris of the above rock (sandstone breccia), and have been brought thither by some torrent or deluge, and that no modern or traditional inundation has reached to such an extent."

In considering the probable agency that has operated in Southern Africa in producing these vast accumulations of gravel, it may be asked, in the first place, have these gravels been laid down by common fluvial action, assisted and increased by floods and rain-storms, such as those at present in operation ? The deluges of rain that sometimes accompany heavy thunderstorms in this country turn every stream, in every ravine, into a dangerous torrent, and the rivers into impetuous floods, that tear away every thing before them, and frequently discolour the sea for many miles with the floating sediment they have brought down with them. But in examining the results of these inundations — the deep and abrupt chasms they have worn, the assorted gravels they have left, the direction and position of the boulders, and the finely laminated mud or clay — there can be no mistaking the agency by which they were effected. With regard, however, to the diamantiferous deposits now under consideration, there are many characteristic features about them that cannot be satisfactorily accounted for by reference to such an agency. The extensive unstratified boulder-gravels, such as are found at Diamondia, Hebron, and many other places, — the unstratified gravelly drift, with clay and boulders, as at Pniel — irregular patches and mounds of boulders, — the boulder-clays, and the confused manner in which they are intermingled throughout the entire length of this river-valley, have made all whose opinions I have been able to obtain declare that such heterogeneous accumulations could not have been formed by South- African river-action under its present conditions. If laid down by this agent, the deposits would certainly have shown a greater regularity ; the silt would have exhibited a regular interlamination of its clays, sand, or gravel as the case might be, such as may be found in the present deposits of the Fish river, in which are imbedded animal and other remains that tell of their recent origin. So also these vast accumulations, had the same conditions existed, would have contained organic remains indicating the