2 PrvESIDEXT's ADDUESS. 



this chorus of thoughts and hopes, these dawning truths, hke 

 great stars just hfting themselves into his horizon, they are his 

 future " — he described very well an impulse on all inquirers into 

 the physical world about them. Whether he was right in calling 

 the half-perceived the best part of truth must be judged by its 

 effect in compelling investigation, but Emerson's maxim will 

 serve me as an apology for choosing climates of former times as 

 the subject of my address; for there are many uncertainties 

 inherent in the methods of the inquiry. The evidence has to be 

 got from many sources, any one of which alone may not take us 

 far. 



Past climates are of interest from several points of view ; we 

 can attempt to reconstitute in mind the conditions under which 

 the former inhabitants of a country lived ; to understand how the 

 present surface of a country became shaped as we find it ; or we 

 may discover whether change in climate is continuous in one 

 direction for a period comparable with one of the recognised sub- 

 divisions of geological time, such as the Pleistocene, and whether 

 we are living in such a period. 



That the climate of what is now South Africa has changed 

 during geological time is as certain as such things can be, for the 

 evidence of the existence of land-ice between the Transvaal and 

 Natal on the one hand and the Tanqua Karroo on the other during 

 the Carboniferous period has been accumulating ever since Dr. 

 Sutherland published his recognition of it in Natal in 1868,' and 

 (hardly a year goes by without fresh facts being discovered which 

 support the theory. In this instance the evidence consists of the 

 preserved effects of the movement of ice over hard rock, and 

 there is an immense body of corroborative evidence in the tillite, 

 or hardened boulder-clay, remaining on that rock and distributed 

 over the country to the south for more than a hundred miles. 

 The evidence is entirely independent of fossil plants and animals, 

 for the characters of the rocks themselves are the only source of 

 information. It was only in very much later times that animals 

 and plants bore such close resemblance to those living to-day 

 that their remains afford satisfactory evidence of climatic condi- 

 tions based on a comparison of their distribution with that of 

 living forms. This instance alone is sufficiently striking to justify 

 inquiry into changes of lesser range, and it is advisable before 

 going further to consider briefly the various kinds of evidence to 

 be expected and searched for in order that we may discuss the 

 relevant facts from South Africa. 



What we call climate is the resvilt of many factors, and a 

 meteorologist could tell us just what the climate was at any 

 particular place and time if he were given the necessary informa- 

 tion about the Sun's radiation, the rotation of the Earth, the 

 distribution of land and water on it and of the air above it at the 

 time in question, but my purpose is only to discuss the evidence 



^ The numbers refer to notes, which are collected together at the end of 



this address. 



