450 CRETACEOUS DEPOSITION AND EROSION 



that still continues ; but, as we shall see, there have 

 been periods of diminished downward erosion during 

 which the rivers widened their valleys and cut exten- 

 sive plains instead of deepening their channels. The 

 river systems south of the main watershed thus de- 

 veloped on a country whose structure has no direct 

 relationship to the origin of the main rivers, and the 

 deep gorges of the transverse streams, such as the 

 Gamka and Gouritz, were cut by the action of the rivers 

 in sawing their way downwards through soft and hard 

 rocks alike as they were exposed. It is certain that 

 the earth-movements of post-Uitenhage age deepened 

 the depression between the Zwartebergen and Lange- 

 bergen, but the movements were greater in some places 

 than others, and were not sufficiently regular in direction 

 and extent to deflect the chief transverse streams into 

 valleys parallel to the mountain ranges. 



In the marine beds of the Uitenhage series we have 

 the inshore deposits of an ocean that stretched from 

 India to South Africa, but its general form is very im- 

 perfectly known. So far as South Africa is concerned, 

 that ocean probably only touched the country and never 

 spread over what is now the interior of the Colony. 

 The next inroad of the open sea is recorded in the 

 Umzamba beds of the south-east coast. The fossils in 

 these rocks are most closely related to Indian forms, 

 and indicate that the beds were laid down at a later 

 stage of the Cretaceous period than the Sunday's Kiver 

 beds. The fact that the Umzamba and the Embotyi 

 beds are faulted down against the Table Mountain 

 series shows that they once extended farther inland 



