THE CRETACEOUS SYSTEM 319 



of a drier climate than had formerly prevailed. 1 Under 

 such conditions the supply of rock debris would be as 

 great as, if not greater than, during the preceding 

 moister period, for the hills would be less protected by 

 vegetation, and the breaking up of the naked rock by 

 change of temperature would proceed rapidly. The 

 occasional rain-storms in such a climate sweep down 

 vast quantities of gravel and sand, rounding off the 

 edges of the rock fragments and thus producing pebbles 

 and boulders of the ordinary shapes. The prevalence 

 of unfossiliferous red-coloured conglomerates and sands, 

 especially near the base of the series, in Uitenhage, 

 Oudtshoorn, Heidelberg, Swellendam, Eobertson and 

 Worcester, supports this explanation ; and the irregular 

 piling up of much of the red rocks is evidence in the 

 same direction. 



The grey shales and muds of the Wood beds in the 

 Uitenhage Division were probably formed in the waters 

 of a river that had direct communication with the sea, 

 for the oyster shells, the Gastroohcena in the logs of 

 wood, and the Pecten, all found in the Wood beds near 

 Dunbrody, point to the proximity of the sea. The 

 plant-bearing shales near Herbertsdale, and the grey 

 shales with Estheria and the other fossils previously 

 mentioned in the Heidelberg area, have not yielded any 

 proof that the water in which they were laid down was 

 in close proximity to the sea. These beds may have 

 been formed in shallow lakes or lake-like expansions of 





1 For an excellent account of the rocks formed under desert condi- 

 tions, such as here spoken of, the student able to read German should 

 peruse Prof. J. Walther's Denudation in die Wttste. 



