TRANSACTIONS OF SECTION C. 40? 
3. Evidences of Glacial Conditions in Permo-Carboniferous Times 
in the Transvaal. By Epwarp T. Metnor, B.Sc. 
(Communicated by permission of the Director of the Geological Survey 
of the Transvaal.) 
The present paper gives a brief account of recent work in connection with 
the rocks at the base of the Karroo System in the Transvaal, including some 
additions to the evidence of extensive glacial action in early Karroo times. The 
description given of the character and mode of occurrence of the glacial con- 
glomerate is based mainly upon observations made in the course of mapping a 
district lying between the Elands and Wilge Rivers, east of Pretoria. ‘The 
Karroo System does not here attain so complete a development as in the more 
eastern and southern portions of South Africa. The whole thickness of the forma- 
tion 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 con- 
glomerate which forms its base. They are occasionally entirely composed of this 
conglomerate owing to the complete denudation of the overlying sandstones and 
grits, 
The upper and well stratified portion of the formation lies everywhere 
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 com- 
paratively recent origin. ‘here is abundant evidence that they were laid down 
upon an old land surface possessing considerable variety uf 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 conglomerate itselt 
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 Red Granite which occurs extensively further 
to the north. 
The boulders are always highly polished and usually facetted. When com- 
posed 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. On 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 is occasionally greenish in colour. Locally there occur in the 
conglomerate lenticular patches of fine-grained, massive, white or cream-coloured 
sandstones, and white, finely laminated shales and mudstones. 
The progressive denudation of the glacial conglomerate exposes at its margin 
the glaciated surfaces of the underlying rocks, which frequently show very clear 
