b PRESIDENT S ADDRESS. 



discussed. Their width ranges from a few yards to a few miles. 

 They have flat floors and they generally have no outlet.'" There 

 can be little doubt that wind alone can start their formation in 

 flat country, and it is aided by increasing brakness of the ground 

 in a depression, for growth of protective vegetation is thereby 

 hindered and eventually prohibited. The important part played 

 by animals in the formation of certain kinds of pan'^ has been 

 abundantly illustrated by Passarge. In a humid climate pans of 

 erosion cannot form, and were a pan-veld to become well supplied 

 with water the pans would eventually either be filled up by 

 material washed into them or, in the event of their being filled 

 to overflowing with water, they would eventually be drained by 

 streams cutting back into them. The presence of horizontal beds 

 is certainly a favoui'able condition for their formation. 



The forms produced by erosion and deposition under glacial 

 conditions need not detain us long; they are characteristic both 

 in mountainous country and on plains, but they have not been 

 produced on the post-Cretaceous surface of South Africa. 

 Though it is occasionally stated that evidence of former glaciers 

 is to be seen in the higher parts of the country, no confirmation 

 has been obtained in the course of the Geological Survey, and 

 1 am permitted to say that during their recent visit to Mont 

 aux Sources Professor Daly and Dr. Wright found no evidence 

 of that kind. 



Evidence from Fossils. 



The palffiontological evidences of climate are difficult 

 to interpret; plants afford more information than animals because 

 the preservation of their tissues allows botanists to draw con- 

 clusions about transpiration, which may throw light on climate; 

 but well-preserved plants' are rare. The value of a comparison 

 of the distribution of fossil species and their living relatives 

 decreases as we go back in time, but a large part of the infor- 

 mation about the climate of late Tertiary and Pleistocene times 

 in Europe depends upon evidence of this kind, and it has been 

 skilfully combined with that from the work of ice. Evidence 

 of this Idnd is open to suspicion; from the bones of the mammoth 

 probably no anatomist would suspect that it differed greatly in 

 its habitat from its living relatives in tropical and temperate 

 regions, but the frozen carcases in Siberia prove that it lived in 

 a cold climate and was specially protected against the effects.^- 



HisTORicAL Evidence. 



Historical evidence of course affects only a^ short 

 period, but it should give proof, had there been considerable 

 and continuous chancre in one direction. Tt_ has often been 

 appealed to, especially concerning north Africa and Asia, and 

 the controversies illustrate the fact that climatic changes may 

 not have been the cause of the shifting or decrease of popula- 

 tions, which have been put forward as one of the strongest 

 evidences of change." 



