president s address. 7 



Post-Cretaceous Climates. 



It is my purpose to-night to consider the South African 

 evidence from post-Cretaceous times only, and an attempt must 

 be made to picture the geographical conditions at the end of 

 the Cretaceous period. The approximate position of the shore 

 hne at that time is known only in the east and south-east, 

 where late Cretaceous shallow-water marine deposits occur near 

 East London and are also perhaps preserved in Bathurst, 

 Alexandria and Uitenhage.*^ Inshore deposits of a slightly 

 earlier age are better known over a much longer stretch of coast 

 to the north-east,'^ and early Tertiary inshore beds are known 

 to exist in Zululand and Portuguese territory, but precise infor- 

 mation about them is wanting.'^ The later Cretaceous beds lie 

 on eroded surfaces of various formations from pre-Cape possibly 

 to the Uitenhage series. South Africa had become an area of 

 denudation rather than of deposition at the close of Karroo times, 

 probably during the Jurassic period. The greater part of its 

 surface was not diversified by mountains or considerable hills; 

 some at least of the northern ranges, such as the Langeberg and 

 Magaliesberg, were probably buried under Karroo beds, but the 

 southern ranges of the Cape were in existence in early Cretaceous 

 times" though less prominent than to-day, and the post- 

 Uitenhage faults had the effect of increasing the relative eleva- 

 tion of the ranges; an approximate later limit to the age of the 

 faults has not yet been determined. A large area south of the 

 main watershed in the Karroo must have been covered by 

 Uitenhage beds, but how far north of the Zwartberg-Zuurberg 

 line they extended is not known; it seems probable, however, 

 that the rivers going to the soxith, the rivers now represented by 

 the Gouritz and Gamtoos, ran over these early Cretaceous beds 

 for a great part of their courses. By late Cretaceous times 

 Bushmanland had been partly stripped of its covering of Karroo 

 deposits.'* The average lie of the land as regards sea-level can 

 be surmised from the present position of remnants of a pene- 

 plain in the interior of the country relatively to the known 

 position of the latest Cretaceous shore lines, bearing in mind that 

 the inshore Cretaceous beds rest appai-ently undeformed against 

 the already bent eastern outcrops of the Upper Kari'oo beds in 

 the Lebombo range.'* It is as yet difficult to estimate sub- 

 sequently produced differences in relative level due to bending 

 as contrasted with block uplift of the sub-continent, but it 

 certainly appears probable that the peneplain was formed at a 

 very considerable elevation. In the Stormberg and Griqualand 

 West this peneplain now lies some 4,600 feet above the sea and 

 the date of its formation has been assigned to the late Cretaceous 

 or early Tertiary.-" Support for this view is obtained from the 

 valley leading from Bushmanland and to Henkries on the Orange 

 River, where Dinosaur bones were found at the bottom of a well 

 about 3,500 feet above sea-level, buried under 110 feet of granite 

 wash.-' The granite floor exposed in the well must be looked 

 upon as the floor of a Cretaceous or early Tertiary valley. No 

 fossils have yet been found in the material forming the 4,600 



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