Pernio- Carhoniferotis Glaciation in Transvaal. 83 



complete a development as in the more eastern and southern portions 

 of South Africa, The whole thickness of the formation rarely 

 exceeds 400-500 feet, and it is not possible as yet to recognise the 

 many divisions which it presents in those parts of South Africa 

 where it attains a much greater thickness. Outliers along the 

 margin of the main area occupied by the Karroo System afford good 

 opportunities for the study of the glacial conglomerate which forms 

 its base. They are occasionally entirely composed of this con- 

 glomerate owing to the complete denudation of the overlying 

 sandstones and grits. 



The upper and well stratified portion of the formation lies every- 

 where horizontally, and its base maintains a very constant elevation 

 of about 4,900 to 5,000 feet. The glacial beds of the lower portion 

 of the formation rarely show distinct stratification, and outliers 

 consisting of these alone closely resemble, both in appearance and 

 mode of distribution, patches of glacial drift of comparatively recent 

 origin. There is abundant evidence that they were laid down upon 

 an old land surface possessing considerable variety of surface feature, 

 and some of the thickest deposits of glacial conglomerate occur in 

 valleys or below escarpments which were in existence before its 

 deposition. 



Owing to the abundant sandy drift arising both from the con- 

 glomerate itself and from the grits and sandstones which usually 

 overlie it, the solid conglomerate is rarely exposed at the surface. 

 Where seen, it is of a light yellow or cream colour, and usually 

 consists of a sandy-looking matrix containing abundant boulders and 

 pebbles distributed without definite arrangement through the mass. 

 The pebbles and boulders vary in size from 2 to 3 inches up to as 

 much as 10 feet in diameter. The materials of which the boulders 

 are composed vary much in character. There is always a great 

 preponderance of local rocks, with an admixture of others which can 

 be shown to be derived from comparatively distant sources, which 

 are to the north of the present position of the boulders. In the 

 district here specially referred to, the majority of the boulders 

 consist of hard red quartzites and conglomerates derived from the 

 Waterberg Formation, which underlies the glacial conglomerate over 

 a large part of the area. Almost equally numerous are boulders of 

 the Eed Granite, which occurs extensively further to the north. 



The boulders are always highly polished and usually facetted. 

 When composed of fine-grained rocks, such as felsites and shales, 

 they frequently show striations on the facets. The matrix of the 

 glacial conglomerate consists of sharply angular fragments of quartz 

 and of rocks similar to those of which the boulders are composed, 

 varying in size from mere grains upwards. It differs to some extent 

 from the matrix of the typical Dwyka conglomerate of the more 

 southern portions of South Africa in presenting an appearance much 

 less suggestive of an igneous origin. By weathering, the matrix 

 of the conglomerate usually gives rise to sandy products ; in some 

 localities, however, it produces a yellowish clay, in which the 

 boulders remain embedded. In specimens from a depth, the matrix 



