president's address. 39 



fairly representing the actual state of matters. A fluctuation in 

 the outflow of heat of 10 per cent, would be equivalent to 1 lb. 

 more or less water evaporated per square mile per minute. It 

 may be safely said that one active volcano will dispose of more 

 heat in a day than many hundred square miles of earth surface 

 in a year. 



That the glaciation of the earth's surface at any period since 

 palaeozoic times cannot have been more than partial, is evident, 

 for were this condition to extend over the entire tropical regions 

 there would remain no sanctuary for the higher forms of life, 

 with the result that all plants and animals unable to withstand 

 the rigours of an arctic climate would perish. That this has 

 not been the case is amply proved by the known continuity of 

 highly developed organisms succeeding one another through long 

 geological epochs covering numerous periods of glaciation. Dar- 

 win was much impressed with the importance of glacial mutation 

 as explaining the present distribution of Alpine organisms.* 



The plants, for example, found in Alpine regions everywhere 

 over the earth's surface, bear a striking resemblance to one 

 another, indeed, identical species may be found in places widely 

 separated by tracts of country having a climate utterly prohibi- 

 tive of migration for these, Alpine plants being peculiarly intol- 

 erant of other than Alpine conditions. The flora of high latitudes 

 is truly Alpine in character, and similar plants are found flourish- 

 ing on the European Alps and in the regions fringing the Polar 

 Seas. Any change of climate one way or another must have 

 been gradual. If we imagine an era of glaciation spreading 

 towards the tropics, we can see that for long periods the low 

 level areas would have a climate quite suitable for the growth of 

 Alpine types. In fact the lower levels would constitute a haven 

 for the Alpine flora driven from the mountains by perpetual 

 snow and ice, and thus a region for mingling and for migration 

 would be provided. With the gradual return of genial condi- 

 tions the plants would migrate back to the mountain fastnesses 



• Origin of Species, 6th ed., p. 330. 



