4 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [NoV, 8,
the north bank of the Orange River, between Bethulie and Jager's Fontein. The sandstones continue beyond the shales (just as we find them on the southern or Great-Winterberg boundary of the same basin), and are visible in the ridges in the direction of Albania, to the north, and of Hopetown, to the south of the same river.
At a drift (ford) on the Reit River, a short distance beyond Jager's Fontein, a mass of rock, which has been termed "clay-slate," makes its appearance. It is of a dark blue slate-colour, and is said to break with a slaty fracture. It is possible that this may be a schist more ancient and indurated than the shales of the Stormberg formation. Beyond this the greater part of the country is covered with calcareous tufa, on which in some places is a reddish sandy soil, about 2 feet thick. The ground is traversed by numerous dykes, and by other slight ridges which seem to be composed of metamorphic rocks. On a near approach to the Vaal River the direction of these ridges can be easily traced; and they all appear to trend E.S.E.-W.N.W. In many places quartz-reefs run parallel with the dykes, their thickness varying from a few inches to 15 or 16 feet. No satisfactory conclusion, however, can be arrived at with regard to the basement rocks which intervene between Jager's Fontein and Pniel, except that none equivalent to those met with in the upper portion of the Stormberg-basin are to be found there. This part of the country, therefore, in all probability formed a portion of the northern or north-eastern boundary of the great sandstone and shale-system of the Stormberg. (See the paper by Mr. Stow, read before the Geol. Soc. Dec. 7, 1870, Q. J. G. S. vol. xxvii. p. 523.)
The immense extent of the diamond-deposits seems to be most clearly proved by the widely separated localities in which they have been found (see Map, Pl. I.). Taking Pniel as a central point, we find that they have been discovered (July 1871) not only at Jager's Fontein, a place nearly 96 miles on the southern side of the Vaal, but also at Mamusa, 75 miles beyond it. At this latter place a diamond upwards of 70 carats in weight was picked up on the surface. How much further these deposits may extend in the same direction is not known; but even this distance gives a breadth of 171 miles. The diamond-bearing country already ascertained stretches down the Vaal River for a distance of 110 miles, to a spot considerably below its junction with the Nu Gariep, or Orange River; whilst, above Pniel, diamonds have been found at a considerable number of places as far as Bloemhof, 102 miles further up the stream; and the last reports (July 1871) state that diamonds have been discovered at least 100 miles nearer the sources of the river, a distance of quite 312 miles from the most southern point previously mentioned.
hypothesis advanced in the 'Geological Magazine,' will be found on comparing these papers. I must add that a great store of useful information about the diamond and the geology of diamond-fields in Australia, India, Brazil, and elsewhere, has been brought together by the Rev. W. B. Clark, M.A., F.G.S., Vice-President of the Royal Society of New South Wales, in his Anniversary Address to that body on May 25, 1870 (8vo, Sydney, 1871). — T. R. J.
