SUN AND CLIMATIC VARIATION 47 



in which the Caledonian chain attained its greatest height. 

 At that date there were not only polar glaciers, but glaciers 

 comparable to those which, later on, marked the approach of 

 the quaternary period subsequent to the formation of the 

 Alpine-Himalayan chain. These glaciers were perpetuated at 

 the base of the Cambrian formations in Norway, in the Yang- 

 tse district, in India, at Simla, and in the south of Australia. 

 This, as we have already pointed out, is no reason why 

 we should believe that the climate became cold at this epoch ; 

 for even to-day there are glaciers below the equator. 



With these reservations we may here summarize the con- 

 clusions reached by geologists as to the climates of the different 

 geological epochs. 



The temperature of the seas seems to have been uniform 

 during the Cambrian Period, and, in fact, there is no reason for 

 assuming — at least, if at that time the orbit of the earth had 

 not become markedly flattened — that this temperature was 

 lower then than during the Silurian epoch that followed. The 

 abundance of corals found at all latitudes in the Silurian seas 

 does indicate warm waters, since the secretion of calcareous 

 matter by marine organisms increases in activity as the 

 temperature rises. No traces of Silurian glaciers have been 

 discovered, but this may simply mean that erosion had levelled 

 the Caledonian mountain chain to such an extent that its 

 mountains no longer accumulated eternal snows upon their 

 summits. There is nothing to suggest that conditions changed 

 during the Devonian Period, though glaciers have been traced 

 at the Cape of Good Hope. On the contrary, corals continued 

 to nourish all round the North Atlantic continent in the region 

 corresponding to the site of the later Hercynian chain in the 

 Central Plateau, Bohemia, etc. In addition, the abundance of 

 red sandstone, whose colour corresponds to that produced 

 in our day in desert regions under the influence of powerful 

 solar radiation, seems to indicate that in those regions 

 temperate to-day the sun's power was then far greater than it 

 is now. The glaciers of the Cape of Good Hope have even 

 suggested the possibility of the South Pole having become 

 displaced by 6o°, but if this were true the same ought to hold 

 for the North Pole, and no indication of such a displacement 

 exists. We must admit, then, that the glaciers of the Cape of 

 Good Hope were the result of a local phenomenon, namely, 



