The Forming of the Drakensberg. 75 



That this vast body of water was not salt is indicated by the 

 absence of marine fossils, the few mollusca known being lamelli- 

 branchs such as Palceomutela. The presence of Esthetics, in both 

 the Beaufort and Stormberg series points, perhaps, to brackish 

 rather than purely fresh-water conditions. 



That the lake was shallow throughout most of the period of its 

 existence is proved by the presence of false-bedding in the sand- 

 stones, and by ripple-marks, rain-prints, sun-cracks, and worm- 

 burrows. Local erosion of the soft beds, with the deposition upon 

 them of coarser arenaceous material — contemporaneous erosion, as 

 it is termed — is met with occasionally, and points to the existence of 

 strong currents. 



Now, as sediment was carried down into the Karroo lake, the 

 latter would tend to become silted up. The great thickness of the 

 Karroo rocks — many thousands of feet — shows that the lake con- 

 tinued to receive sediment during an immense period of time, and 

 yet the depth must have remained much the same all through. 

 This shows either that the water level was continually being raised 

 by the sediment deposited on the bottom of the lake, or else 

 there must have been a general subsidence of the area occupied by 

 the Karroo lake, due either to weighting of the earth's crust by 

 the sediments laid down upon it or owing to elevation of the crust 

 in a neighbouring area. Probably both factors have combined to 

 cause the depression. 



Now, we find that during the formation of the Upper Karroo 

 rocks there were two tracts in which folding and elevation were 

 going on, within the area of the Karroo lake.* 



The first of these tracts is the mountainous country around the 

 Cederberg, to the west of the Karroo, elevated by the continuation 

 of earth movements dating back to pre-Karroo times. 



The second area lies along the south coast of the Colony, and 

 the mountain ranges produced form the Zwarteberg, Langeberg, 

 Zuurberg, &c. The beds are intensely folded in this area, but 

 northwards these folds die out rapidly, and in the central portion of 

 the Karroo the rocks are hardly affected by them. 



The earth-movements which produced these second set of folds 

 have been named by Mr. A. W. Rogers "the Zwartberg move- 

 ments," and, according to him, " took place some time between the 

 period of deposition of the upper part of the Beaufort series and 

 the close of the Stormberg series." f It is apparent that during the 



* Vide Eeports of the Geological Commission, 1896-1903. Cape Town. 

 f A. W. Rogers, "The Geological History of the Gouritz River System." 

 Trans., South African Philosophical Society, vol. xiv., p. 370, 1903. 



