Geological History of the Gouritz Biver System. 379 



which partly fill the depressions between the Zwartebergen and 

 Langebergen, and similar depressions south of the latter range. 

 These rocks extend in places to a level below that reached by the 

 present river valleys. The Gamka Eiver, for instance, south of 

 Calitzdorp, runs across these rocks, and its tributary the Oliphant's 

 Eiver has the Uitenhage Series for its bed rock for a considerable 

 distance. South of Herbertsdale sandstones belonging to the 

 Uitenhage Series form the bed of the Gouritz Eiver for some few 

 miles. Near Mossel Bay the conglomerates at the base of the Series 

 lie below sea-level ; and at Swellendam their base was not reached 

 by a bore hole put down to a depth of 800 feet below the present 

 surface. The evidence afforded by the Uitenhage Series proves, that 

 before these rocks were formed there were deep longitudinal valleys in 

 the south of the Colony, and that the valleys north and south of the 

 Langebergen were not directly connected as at present by a river 

 traversing the latter, for there is no ancient transverse valley in the 

 Langebergen, filled up with Uitenhage deposits. This absence of all 

 traces of pre-Uitenhage transverse valleys in the Zwartebergen and 

 Langebergen, together with the distinct evidence of longitudinal 

 valleys, which were eroded relatively more deeply than the present 

 valleys, affords strong evidence against the view that the Gamka 

 and other rivers from the Karroo were antecedent to the mountain 

 ranges ; in other words, these rivers did not cut their valleys down 

 through the slowly rising mountains. 



The lowest points of the Zwartebergen and Langebergen now rise 

 considerably higher than the highest level of the areas formed by the 

 Uitenhage rocks, but these have suffered a great decrease in area and 

 thickness during the lapse of time from their formation to the present 

 day, during which it is very improbable that they were again 

 depressed below sea-level. It seems likely that they once partially 

 buried the Langebergen and Zwartebergen under the load of debris 

 derived from these ranges, and, in the later stages of their deposition, 

 from the country to the north which is now the Karroo. The result 

 of this filling up of the pre-Uitenhage inequalities of surface was, 

 that the rivers which were flowing southwards from the then recently 

 formed watershed flowed south over the present position of the 

 Zwartebergen, across the area of deposition as this gradually became 

 dry land. Whether the rivers from the southern flank of the 

 watershed formerly discharged into the estuaries and sea, in which 

 the Uitenhage Series were being deposited, further east than the 

 present Oudtshoorn district or in that district will be a difficult 

 point to prove. It is probable, however, that in the later part of the 

 Uitenhage period the rivers did enter the area between the Zwarte- 

 bergen and Langebergen. 



