﻿Vol. 6 1.] THE GLACIAL CONGLOMERATE IN THE TRANSVAAL. 687 



Evidence is plentiful that the Glacial Conglomerate was originally 

 formed on a land-surface possessing considerable variety of feature. 

 The denudation of the Conglomerate frequently exposes ancient 

 escarpments of Waterberg Sandstone, the uppermost beds of which 

 are often glaciated, while the Conglomerate on their southern slopes 

 is as a rule especially rich in very big boulders. In other cases 

 the Conglomerate fills old valleys, which are now in process of 

 re-excavation, such as the valleys of the Wilge River and Bronkhorst 

 Spruit. 



The Waterberg-Sandstone Formation, which consists of a suc- 

 cession of conglomerates and sandy strata of extremely-various 

 degrees of hardness — from soft sandstones to very resistant 

 quartzites — almost invariably gives rise to landscapes of con- 

 siderable diversity, including some of the most rugged and 

 picturesque scenery in the Transvaal. In the district shown in 

 the map (fig. 1, p. 680) between the Elands and the Wilge Rivers, 

 however, where the removal of the overlying Karroo glacial deposits 

 is still in progress, the Waterberg ridges continue to retain outlines 

 characteristic of glaciated areas. 



In the district here dealt with, the Glacial Conglomerate occurs 

 at all levels within a range of about 350 feet, its lower limit 

 varying with the contours of the underlying surface of older rocks. 

 Its upper limit, marked by its junction with the horizontal beds 

 of the Upper Karroo or High- Veld Series, occurs very regularly 

 at an altitude of about 4900 feet above sea-level. 



Glaciated Rock- Surfaces. 



The surfaces of the older rocks underlying the Glacial Conglo- 

 merate frequently present very clear evidence of glacial action. 1 

 The outcrops of the hard quartzites of the Waterberg Formation or 

 the Pretoria Series, which formed part of the land-surface upon 

 which the Glacial Conglomerate was laid down, are frequently 

 rounded- off, polished, and sometimes very clearly striated. The 

 constant alternations of heat and cold to which all rocks are sub- 

 jected in the South African climate leads to the rapid destruction of 

 brittle rocks, such as quartzites. Consequently the glaciated surfaces 

 are broken up on exposure, and are only found on the immediate 

 margin of the patches of Glacial Conglomerate, where the underlying 

 rocks have been exposed comparatively recently. A typical example 

 of these glaciated surfaces is shown in fig. 4 (p. 686). Such glaciated 

 surfaces have been found distributed over an area of some 300 

 square miles, as shown in the accompanying map (fig. 1, p. 680). 

 It will be seen from the compass-readings tabulated on the 

 following page, that the striae exhibit a remarkable constancy of 

 direction. 



1 E. T. Mellor, 'On some Glaciated Land-Surfaces occurring in the District 

 between Pretoria & Balmoral ' Trans. Geol. Soc. S. A. vol. vii (1U04) p. 18. 



