Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/22

6 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 8, spersed throughout, bound together with a calcareous cement; as is the case at Hebron and Diamondia (figs. 1 & 2, c). These gravels, wherever found, contain large quantities of small fragments of fossil wood.

3rd. Irregularly stratified gravelly clays of various colours. Some of these also contain irregular patches of boulders. Examples of these are met with at Hebron and Diamondia (fig. 2).

4th. A pebbly drift, without large boulders, and bound together by a red ferruginous and rather clayey matrix. This is the case at Jager's Fontein.

5th. A gravelly sand of different shades of colour; the upper generally white, with irregularly interspersed boulders. This de- posit is rather contorted in some places, and is found at a much lower level than the others.

Section I. I have not been able to procure many sections. One of them (fig. 1) comprises Natal Kopje, Cawood's Hope, and Gong- Gong; from all of which places many diamonds have been procured.

Natal Kopje. — On the summit of Natal Kopje there is a dark blue gravelly clay, with boulders (1); below this is a yellowish clay, inter- mixed with calcareous tufa (2); and beneath this is a reddish, ochreous, gravelly clay (3). These clays are very irregular in thick- ness, altering very much in a short distance; their total thickness varies from 2 to 4 feet. The largest diamonds (up to the present date, July 1871) have been here found within a couple of feet of the surface.

Below these beds is a great deposit of gravel (d). Its true thickness has not been ascertained; but shafts have been sunk into it for upwards of 30 feet without reaching the bottom; it is probably much thicker. It contains multitudes of pebbles of the various rocks found in the diamond-deposits. The peculiar shape, rather flat and oval, which many of them have, has caused the diggers to name them "kidney-stones;" they are thickly packed together in some portions of the gravel.

Upon what rocks this deposit rests is not known; but connected immediately with it is a subterranean escarpment of a rock (a) called by the diggers "rotten-stone" ("decomposed felspathic trap," Jones ), which they describe as a kind of "cone-within-cone," decomposed, rotten sandstone, breaking up in concentric layers, with hard, firm nuclei, resembling boulders. A shaft has been sunk down the face of this underground precipice for upwards of 30 feet, as shown in the section (fig. 1). Dense patches of such large pebbles as are found in the gravel seem to be massed along its front. This rock slopes off towards the land side, and is there covered with gravel (e), and boulders are spread over the surface. This gravel is about 2 feet thick; as yet no diamonds have been found in it.

Cawood's Hope. — Joining the Natal Kopje at rather a lower level, are two smaller kopjes, composed of a deposit similar to that found iu the Natal Kopje. At the foot of a small ravine leading from these