F. P. Mennell—The Rhodesian Banket Beck. 359 



pebble in the clay of the same pit. Possibly, therefore, wind action 

 was not rare ; its traces may even prove sufificiently common to 

 warrant the inference that steppe-like conditions then extended 

 to those parts of the country. The other evidence in favour of that 

 view need not be repeated here ; but it should be borne in mind, 

 for, as pointed out in my previous paper (p. 415), what is good 

 proof of wind abrasion is not in itself a necessary proof of steppe or 

 desert conditions. 



The pebble herein described remains in Mr. Brown's collection, 

 but he has kindly allowed the Geological Department of the British 

 Museum to take plaster casts of it. For this, and for his courtesy in 

 submitting the specimen to me, he has my sincere thanks. 



IV. — The Ehodesian Banket Beds. 



By F. P. Mennell, F.G.S., Curator of the Rhodesia Museum, Bulawayo. 

 I. Introduction. 



WHAT are popularly termed the Banket Beds of Johannesburg 

 have for years past been justly celebrated for their extra- 

 ordinarily large and steady gold production. Their literature has 

 already assumed formidable dimensions, so it is unnecessary for my 

 present purpose to give a detailed account of the features thfey 

 present. They form part of what is generally known as the 

 Witwatersrand Series, which consists of highly altered sandstones 

 and conglomerates almost certainly of Archaean age.^ They uncon- 

 formably overlie the banded rocks known as the Hospital Hill Beds, 

 and are overlain by the Dolomite, often termed the ' Olifants Klip ' 

 or * Elephant Eock.' 



The gold in the Eand banket is not found in independent veins or 

 reefs. It is confined to a few more or less constant horizons 

 (universally but erroneously termed ' reefs') in the rock itself, but 

 at the same time the latter is highly impregnated with silica and 

 pyi-ites, and it is these cementing materials, principally the pyrites, 

 which carry the gold, while the pebbles are practically non- 

 auriferous. It thus appears that the absence of true veins is 

 due to the ease with which solutions could spread through the 

 originally incoherent gravelly material, instead of their flow being 

 confined to cracks and fissures. The constancy of horizon may 

 therefore be attributed merely to the localization of precipitants. 

 It is certainly not due to the gold being detrital like the other 

 materials of the rock : regarded as ore deposits the Eand veinstones 

 are in no sense ' alluvial.' 



II. The Old Rhodesian Conglomerates. 



I first drew attention to the occurrence of conglomerates among 

 the presumably Archsean rocks round Bulawayo in the Ehodesia 



^ See discussion of age and correlation, Geol. S. Ehodesia, pp. 20-25. 



