62 Cretaceous Rocks of Pondoland 



bush covered slope, rising 50 or 60 feet above sea level. It is possible 

 that the Cretaceous rocks are the foundation there, but they are only 

 exposed along the river bank. On the left bank, the cliffs lie half a 

 mile to the North-east, the intervening space being covered by sand, 

 on which there is a tolerably thick growth of the usual low coast bush. 

 These cliffs are much higher than on the other side, there being 52 

 feet of visible outcrop above the basement conglomerate. At this 

 spot there must be more than 30 different alternating beds. 



The accompanying section represents the finest exposure. The 

 beds are not all continuous, nor can they be called unconformable. 

 Following them along the line of outcrop they thin out in places and 

 come in again further on. Bed 1 is visible for the whole length of 

 exposure at low tide, and is also probably the basement on the right 

 bank of the river. Beds 3, 4 and 10 as also No. 2, vary in thickness 

 but can be traced throughout the whole length of cliff. The strata 

 above 20 were not accessible during the time at our disposal ; but, 

 from the beach, they appear to be similar to those below. 



Throughout the whole series certain mollusca prevail. As shewn 

 on the section there is a constant alternation of beds of calcareous 

 sand and of shell limestone. The sandy beds show dark brown on 

 exposure and are in a very friable condition when weathered. When 

 broken open they are found to be much harder internally and greyish- 

 blue in colour. The included fossils are mostly decomposed, the 

 calcite of the shell being represented by a film of carbonate of lime in 

 a powdery amorphous condition. 



Duiing the 'Challenger ' Expedition it was found that the character 

 of the deposits on the sea floor gave evidence of the approach to land 

 even 150 to 200 miles away. The littoral deposits were blue and 

 green muds which became red or brown after being brought up. 

 These muds gave off sulphuretted hydrogen. The blue colour is 

 caused by decomposing organic matter which combines with the 

 sulphates contained in the sea water and reduces them to sulphides. 

 The sulphides react on the Iron and Manganese in form of silicates, 

 and these being very unstable in presence of water and oxygen are, 

 where they lie on the surface, soon transformed into oxides, showing 

 brown and red. The carbonate of lime of shells, especially in the 

 form of arragonite, is broken down during these chemical reactions ■ 

 but where the rock is reached by sea water the sulphates of the ocean 

 seem to reverse the process to some extent, so that while the matrix 



