22 PEOCEBDnSTGS OP THE GEOLOGICAL SOCIETY. [NoV. 8, 



intruded laterally, and between previously existing strata, has re- 

 ceived their impress, and is now the great conservator of the country 

 from the tremendous denudation going on in South Africa, with its 

 excessively dry climate, its intense heat, and its occasional heavy 

 floods. 



The Vacil-R'iver Diamantiferous Region is known to extend from 

 near the town of Potchefstrom, the capital of the Transvaal Republic, 

 down the whole course of the Yaal to its junction with the Orange 

 Eiver, and thence along the Orange River for at least 60 mileso 

 Digging-operations are at present confined to the Middle Yaal, from 

 the residence of the Griqua Chief, Barend Bloem, at Hebron, down- 

 wards on both banks of the river to the Bechuana Kraal of Sibonell. - 

 Along the whole course of the Vaal there is the same general 

 development of trap, consisting of basalt, amygdaloids, trap-porphjry, 

 trap-conglomerates, and associated metamorphic rocks. Granite 

 exists nowhere in situ ; but granite nodules occur in the trap conglo- 

 merate. Syenitic greenstone is developed in one of the localities near 

 Klip drift, and seems to be the foundation rock there. 



Sedimentary rocks, sandstones, limestones, &c. occur in some of 

 the Kopjes (hUls or heights) capped by basalt. 



The soil on the summits of the rocky hillocks consists of a ferru- 

 ginous loam and imbedded water-worn pebbles. These pebbles and 

 the loose boulders exhibit the appearance of having been water- worn 

 for a considerable time. They are mainly of basalt, amygdaloid, 

 sandstone, agate, peridot, garnet, tourmaline, quartz, jasper of various 

 colours, granite, binary granite, serpentine, malachite, gneiss, &c. 



It is to be noted that the alluvial soU prevails everywhere on the 

 tops of the rocky hillocks, considerably above the present river-bed, 

 and extends inland from the river for two and three miles, and in 

 some cases much further. The hollows are filled with drift sand ; and 

 underneath, the pebbly mass is imbedded in a stiff clay, which is 

 most difficult to work by the ordinary washing processes carried on 

 by the diggers, and accordingly has been neglected for the easily 

 washed material of the sides and summits of the heights. The 

 summits are in greater favour than the sides amongst the diggers ; 

 and no doubt the wealth of the sides has found its waj'' into the 

 hollows and probably into the gravelly bed of the present river-course. 



The history of one digging-centre in the Yaal, Cawood's Rush, 

 supports this opinion. This spot is a low-lying gravelly bank ; and 

 the river sweeps round the greater part of it, so as to form it into a 

 species of peninsula. The old Avatercourse was undoubtedly across 

 the isthmus, where large and very ancient trees still live, indicating 

 the former bank of the river to have been there. The trees around the 

 present bank are all young. When, therefore, it is understood that 

 these trees only occur flanking streams, it is manifest that the 

 peninsula of CaAVOod's Hope was formerly an island, and that at a 

 very recent period it Avas the river-bed. It proved a place of un- 

 exampled success in the diamond-findings of South Africa. Shells 

 of the genera Anodon and Oyclas, which live in the Yaal, Avero dug 

 up in every part of the spot with the epidermis stiU on. The gravel- 



