MODIFICATION OF THEORY EXAMINED. 85 



rays, instead of being warmer than at present, would 

 in reality be far colder ; for this reason, that the 

 temperature of a snow- and ice -covered country can 

 never rise much above the freezing-point. As an 

 example of this I pointed out that, 'were it not for ice, 

 the summers of North Greenland would be as warm 

 as those of England (whereas in point of fact they are 

 colder than our winters) ; and that were India covered 

 with an ice-sheet, its summers would be colder than 

 those of England.' 



" Another point," he says, " of great importance in 

 connection with this subject is the fact that this 

 permanent storing-up of cold depends entirely on the 

 annual amount of snowfall in proportion to that of the 

 sun- and air-heat, and not on the actual cold of winter, 

 or even on the average cold of the year." This I have 

 shown at considerable length in Chapter III., is one of 

 the most widespread and fundamental errors within the 

 whole range of geological climatology. Perpetual snow, 

 instead of being due "entirely" to the annual amount 

 of snowfall in proportion to the quantity of heat 

 received by the snow, is in most cases not even mainly 

 due to this cause. The overlooking of the fact that 

 in the conservation of snow the temperature of the 

 snow itself is one of the main factors has been a 

 fruitful source of error. 



High Land and Heavy Snoivfall in relation to the 

 Glacial Epoch. — According to Mr. Wallace, "high land 

 and great moisture" are essential to the initiation of 

 a glacial epoch. Undoubtedly high land and great 

 moisture are the most favourable conditions for 

 bringing about a glacial state of things ; but I can 

 hardly agree with him that they are necessary and 

 indispensable. 



As to the second of these conditions, great moisture 



