■PRESIDENTIAL ADDRESS. SECTION B. 35 



This dogmatic statement could hardly have been made had its 

 author been able to investigate the facts for himself, but as it 

 unfortunately happens that the evidence so far discovered lies 

 in rather remote regions — India, China, Australia, South 

 Africa, Norway, Canada, South America — preconceived notions 

 of what ought to have been have prevented the acceptance of 

 evidence quite as good as that which leads men to believe that 

 anthracite is of vegetable origin. 



South Africa has, so far as we know at present, a fuller 

 record of glacial periods than any other part of the world, for 

 on three distinct horizons there is good evidence of glacial 

 conditions. The earliest, that in the Lower Griqua Town 

 beds, is a tillite with striated boulders, which is nearly lOO feet 

 thick in places and extends from the Orange River to Made- 

 bing in Bechuanaland. Unfortunately we are at present in 

 ignorance as to its age, and beyond saying that it must be 

 older than the Devonian nothing definite can be stated. The 

 evidence for the second glacial period is very restricted at 

 present, being confined to a strip of country about 23 miles 

 long in Clanwilliam, with a probable outlier on the top of 

 Table Mountain. This evidence is also in the form of a tillite 

 and striated boulders, probably of late Silurian age. The third 

 period is represented by the Dwyka tillite known in all the 

 territories south of the Zambesi, and the underlying glaciated 

 surfaces north of the Karroo. This glaciation occurred in 

 late Carboniferous, or possibly early Permian times, and cor- 

 ^ponding rocks, which may well be considered contem- 

 ^raneous with our Dwyka, are known in India, Australia, 

 and South America. 



The question of the cause of this remarkable extension of 

 glacial conditions in low latitudes has not been solved, though 

 several attempts have been made. The facts are now fairly 

 well known, and the glacial explanation is generally accepted. 

 Their importance for our present purpose is that they negative 

 the view that a gradual change of climate in one direction has 

 prevailed; there was, as far back as we can trace the evidence, 

 no universal climate, warm or otherwise, out of which the 

 climatic zones of to-day have developed. The cold conditions 

 have been ascribed to two sets of causes; alteration in the com- 

 position of the atmosphere, by which less hindrance was placed 

 in the way of the escape into space of the dark heat-rays from 

 the earth's surface, and changes in the amount or nature of 

 the rays received from the sun. It has been shown by obser- 

 vation that the heat received from the sun alters in amount 

 within comparatively short periods, and also that a variation 

 in the quantity of carbon dioxide in the air must affect the 

 air's power of preventing the escape of heat; but the great 

 difficulty in the way of these explanations is that they must 

 apply to the whole surface of the earth, while the glacial condi- 

 tion were, so far as is known, confined to certain areas. For 

 instance, if any such hypothesis be put forward to explain the 

 Pleistocene glaciation, a difficulty arises from the fact that no 

 sign of glacial conditions in those times has been discovered 



