470 Annals of the South African Museum. 



ration of the sandstones, shales and mudstones which is predominantly 

 red or reddish-purple. Even those sandstones which appear pale in 

 the field prove, when freshly fractured, to have a decided red colour; 

 and frequently, as along the northern face of the Wittebergen near 

 the village of Hersohel, and at Lady Grey, the mudstones are bril- 

 liantly crimson. In the Herschel division and in Aliwal North, the 

 clays near the base are frequently blue or even grey; but only the 

 few feet or so lying directly above the Molteno Beds show this 

 characteristic; they soon give place to typically red deposits. 



The climatic significance of red is a subject which has engaged 

 the attention of several workers, especially in America, where the 

 development of the Permo-Carboniferous Red Beds and the Triassic 

 Red Beds has stimulated research. Barrell, discussing the subject 

 in 1908, considered that red colours of sediments are due to oxidation 

 at the time of origin of the sediments, ferric oxide being a component 

 part of the accumulating deposits. He pointed out that in moist 

 climates, heat and exposure all tended to the production of red soils, 

 but that red was also a feature of some deserts. He concluded that 

 the chief condition for the formation of red shales and sandstones is 

 merely the alternation of seasons of warmth and dryness with seasons 

 of Hood, by means of which hydration is accomplished. This supple- 

 ments decomposition at the source of the rock-waste and that which 

 takes place in transportation in rivers. Wetting, drying and oxidation 

 decompose the original iron minerals and remove all traces of carbon. 

 Red shales and sandstones may thus originate in rainy, sub-arid or 

 arid climates without any close relation to temperature, and typically 

 as fluvial and pluvial deposits upon land ; but the origin of such rocks 

 is most favoured by climates which are hot and alternately wet and dry. 



The same author in 1913 pointed out that redness in rocks is no 

 criterion for the the separation of humid from arid climates, although 

 red beds are frequently the accompaniments of aridity. 



C. W. Tomlinson, in 1906, dealt with the conditions of origin of 

 the Red Beds of Western U.S.A. He states "Where alternations of 

 light- and dark-red strata occur, the more' deeply coloured beds are 

 in most cases of liner grain than the others. The occurrence of 

 coarse-grained massive bull' sandstones in a series of maroon or cho- 

 colate shales has been noted by many writers. This association holds 

 true in many other Red Beds besides the group here under con- 

 sideration. Thwaites reports it as an almost unfailing relation in the 

 Lake Superior sandstone series of Northern Wisconsin, and Geikie 

 mentions its existence in the Triassic New Red Sandstone of Gt. Britain". 

 Further, "the colour of prevailing red strata in the Red Beds series 



