ORTGIX OF RAXD IIANKETS. 55 



The Uitenhage System. 



The basement series of this system consists of gravels known 

 as the Enon Conglomerate. At the base there are some 1,500 

 feet. of red conglomerate, followed by some 500 feet of white 

 conglomerate. The pebbles are of white quartzite, averaging 

 in the Red Enon about the size of a duck's egg, but occasionally 

 being as large as one's head ; the pebbles of the white Enon are 

 sometimes the same as those of the red, 'but occasionally are, 

 over wide areas, very much larger. The matrix is gypsiferous 

 clay, in the red variety stained with iron. This enormous de- 

 posit of gravel is the direct result of the folding of the coastal 

 ranges of mountains. So far it has only been found on the 

 sea-ward side of them, but it is possible, as it is found in the 

 valleys between the ranges, that it may have been formed on 

 the landward side as well, but has subsequently been swept away 

 by denudation. It is found from Uitenhage to Worcester, a 

 distance of 550 miles, and though showing considerable varia- 

 tions, is in the main characterised by the same features. Usually 

 the gravels are water sorted, with pebbles of equal size arranged 

 in layers which may be separated by banks of sand ; at other 

 places, as at Knysna, the Conglomerate may consist of all sizes, 

 mixed with a considerable amount of sandy matrix between, 

 such as in the material formed by avalanches in the Alps. The 

 conditions of deposition are as follows : The coastal ranges had 

 'been recently folded up ; the rocks participating in the folds 

 were the Cape formation, and at any rate the lower members 

 of the Karroo .beds, as these are found on the seaward side of 

 the mountains ; the more superficial rocks were structurally weak 

 from the intense bending, and the mountains were high, pos- 

 sibly snow-capped, and plentifully supplied with water, hence 

 great masses of debris were washed down the sides of the moun- 

 tains. Beneath, there was a flat coastal shelf. The water of 

 the torrents carrying great burdens on the slope, owing to the 

 energy given to the water by the steep descent, was suddenly 

 spread out on the flat at the foot, and the carrying capacity of 

 the water was reduced very considerably ; hence, although the 

 water was sufficient to carry away the finer material from the 

 debris, the larger boulders were left behind. The mountains 

 presently became lower ; water became more scarce, land over the 

 surface of the gravels the rivers carried only sand and mud, 

 frequently ending in lakes, drainage from which was through 

 the conglomerate below. The surface of the gravel was little 

 below sea-level. Hence were formed the lacustrine deposits, 

 aeolian sands and estuarine marls of the second member of the 

 Uitenhage series, the Wood bed. The surface of the land sank 

 still further, and over the whole were laid down the Marine 

 beds, containing abundant ammonites and trigonias, which suffi- 

 ciently date the deposit as Neocomian. On the rising of the land 

 the whole of this loosely compacted series of rocks would have 

 l)een srwept away, as those forming the littoral deposits of the- 



