114 E. T. Mellor — Glacial Conglomerate of South Africa. 



bowlders of very miscellaneous composition, and ranging in 

 size up to a diameter of eight or ten feet. These pebbles and 

 bowlders are frequently facetted, and those of very hard mate- 

 rials are always highly polished, while bowlders of somewhat 

 softer nature, especially if fine in grain, such as hard shales 

 and weathered felsitic rocks, frequently show striations. A 

 network of cracks in some cases divides the pebbles into a num- 

 ber of fragments which have been again cemented into a 

 whole. In any particular locality there is always a prepon- 

 derance of bowlders derived from rocks which locally underlie 

 the Glacial Conglomerate, associated with others easily recog- 

 nizable as derived from more distant sources, which are always 

 to the north of the present position of the bowlders. Thus 

 along the eastern railway line, to the south of an area mainly 

 occupied by the Waterberg Formation and the Red Granite, 

 the Glacial Conglomerate contains an abundance of bowlders 

 derived from these rocks. South of the outcrop of the hard 

 white Magaliesberg quartzites, fragments of the white quartz- 

 ites are very abundant. Those lying nearest to the ridge from 

 which they were derived are angular and frequently of huge 

 dimensions, so that when weathered out and lying on the sur- 

 face they are conspicuous objects at a distance of two or three 

 miles. On the eastern Witwatersrand the conglomerate con- 

 tains many bowlders derived from the Rand Series together 

 with others formed of the hard cherts of the Dolomite to the 

 north. Except quite locally, the lower and more massive por- 

 tions of the conglomerate rarely show any traces of bedding, 

 but are occasionally traversed by irregular partings dividing 

 the rock into rude sheets with undulating billowy surfaces. 

 Towards the upper portions of the conglomerate, lenticular 

 beds of line-grained massive sandstone frequently occur, 

 together with patches of white and cream-colored shales and 

 mudstones. The shales appear to have been formed in local 

 pockets below the ice. They consist of the finest glacial mud. 

 The examination of a district of some hundreds of square 

 miles in extent leads to the conclusion that at the termination 

 of the period during which glacial conditions obtained, the 

 country was left covered with an almost complete mantle of 

 glacial deposits, quite similar in character and distribution to 

 those remaining in other parts of the world from extensive 

 glaciation of more recent date. After the cessation of glacial 

 conditions the conglomerates and associated deposits appear to 

 have suffered a certain amount of sub-aerial erosion and denu- 

 dation, during which materials derived from the glacial 

 deposits underwent re-arrangement and re-deposition, giving 

 rise in some cases to beds of conglomerate very similar in com- 

 position and general appearance to those of glacial origin, with 



