Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/29

1871.] STOW VAAL-RIVER DIAMOIND-GRAVELS, 9 No. 5 is a very dark blue, slate-coloured, gravelly clay, with irregularly interspersed boulders ; below this is No. 6, a yellow clay, thickly mottled with patches of calcareous tufa, which has evidently infiltrated into its substance ; and below this is No. 7, a reddish, ochreous, gravelly clay. These rest upon the same rock (" rotten- stone ") as that met with in the Natal Kopje. The hollows of its surface are termed " pockets " by the diggers ; and in these the finest diamonds are said to have been found.

These gravelly clays seem to be the equivalents of those found above the great gravel-deposit at the above-mentioned kopje. They are also found on the opposite side of the river, at Diamondia, capping the same kind of rock. There are other beds of a very similar character, resting upon the highest of the Hebron gravels (see fig. 2). Continuing this section, a vast accumulation of boulder- gravel (c) is found at rather a lower level. Its width is 300 or 400 yards ; shafts have been sunk to a depth of between 30 and 40 feet without reaching its bottom. It is quite unstratified; and large boulders are confusedly mixed with it. The upper portion is of a red colour ; but, on digging into it, it gradually becomes lighter below, and more compact. In some parts it has a calcareous cement.

On the Hebron side there is also another great deposit of boulder- gravel, at rather a higher level (see fig. 2). This seems to have almost entirely the same cement or matrix as those just mentioned. All these gravels contain diamonds, as well as numerous frag- ments of fossil wood (the specimens sent were obtained at c, on the Diamondia side). Some fragments of fossil bone, found at the same place, have been unfortunately lost ; but, from the description given, they must have been water-worn fragments of reptilian remains *. The pebbles contained in the gravel are illustrated by the specimens sent. See Nos. 10 & 11, from Hebron, and No. 12, from Diamondia, in the Appendix.

The reddish colour of the upper portions of the gravels at c, c, seems to be most probably due to infiltration from above, as, on pe- netrating into them, the colour soon becomes paler, and gradually disappears. The same may also be said of the lower gravels that have a calcareous cement.

Prom the lie of the strata, it is probable that these gravels, c, c, rest upon the ancient rocks marked h, h ; but, for want of definite information, I have been unable to show their exact position with reference to each other. These lower rocks are described by some of my friends as " metamorphic " and distinctly showing evidence of stratification, with a dip of about 7° to W.N.W., towards the river on the Diamondia side, and from it on the Hebron side f.

bone, 1^ by 1 inch, very much polished. July 6, 1871.
 * I have since seen one of these specimens; it was probably a metapodal

t I cannot help thinking that the so-called " clay-slate " of the Vaal is very similar to, if not identical with, rocks of the same character in the lower portion of the Great-Fish-River valley, and that an ancient system of metamorphic rocks, most probably connected with those of the Yaal, underlies the strata of the Stormberg basin ; indeed, judging from what I have seen in some of the exten-