SCIENCE- GOSSIP. 



2,21 



OEOLOGICAL NOTES IN THE OEANGE EIVEE COLONY. 



By Major B. M. Skinner^ R.A.M.C. 



TN a former article (SciBNCE-GossiP, vol. vii., 

 -*- No. 74, p. 135) it was i3ointecl out that Bloem- 

 fontein occupies a p)ositioii where the Karroo 

 strata pass up into the Molteno group of the 

 Stormberg strata. The railway station, level 

 4,517 feet, marks fairly exactly the altitude at 

 which this change takes place. Above this point 

 sandstones predominate, while below mudstones 

 prevail. Borings made below this level show 

 casts of mudstones, chiefly blue grey, sometimes 

 purplish in tint, with thin bands of sandstone, 

 the same condition being seen in the banks of 



that of the modern wildebeeste. This particular 

 spot was a most exceptional one among manv 

 scores of similar diluvia visited, in that, in addi- 

 tion to the horn-core, two shells of a small 

 Siiooinea were found in a carbonaceous layer. 

 Another exception which may be noted was a sec- 

 tion in the stream-bank west of the town, which 

 provided, five feet below the surface, the stone 

 of a peach, lying in a sandy layer of diluvium. 



The result of disintegration of the rocks has 

 been the formation of two classes of soil, sand 

 and clay : there are also soils formed from the 



Bed axd Bank of the Bloemsprdit. 



dongas and in the Bloemspruit. The subjoined 

 photograph, taken in the Bloemspruit about two 

 miles east of the town, shows the bed and lower 

 bank of this stream, where the outcropping rock 

 was of this character. The white band is traver- 

 tine, covering denuded mudstone. Above the 

 travertine is modern diluvium. 



The modern diluvium in this bank — and it is of 

 much the same character elsewhere — varies in 

 places, being sometimes chiefly sand, sometimes 

 clay, or a mixture of the two. In some parts the 

 strata of clay or sand show patches of darker tint, 

 and occasionally of black carbonaceous material, 

 in which the forms of ferns and grasses may 

 be distinguished, generally too friable to be pre- 

 served. Near one of these patches, a little below 

 the site of the photograph, some eight feet below 

 the surface, and embedded in a carbonaceous 

 sandy clay, a horn-core was discovered, resembling 



April 1902.— No. 95, Vol. VIII. 



admixture of these, also a black soil, which is a 

 carbonaceous clay. The last has been formed, 

 whenever found, in localised patches near dolerite 

 hills. It is the result of denudation of dolerite 

 accumulated in an area to which there was no 

 outflow, until the level of the top of the obstruc- 

 tion had been reached, and consequently marks 

 the sites of small bogs. In the present day such 

 patches of black soil are not extensive, and are 

 deeply furrowed by the rush of rain water to lower 

 regions. The pure clay soil is usually found only 

 at the foot of a dolerite hill. It contains boulders 

 of dolerite which are disintegrating, but doing so 

 more slowly than when exposed to air only. Some 

 of these have been denuded through removal of 

 the surrounding clay for brickmaking purposes, 

 and lie in the middle of a clay quarry on the talus 

 slope near New Fort Kop. Seen alone they might 

 be suggestive of other means of production. 



