THE PLEISTOCENE OR GLACIAL PERIOD. 437 



retention of solar radiation, abetted by an increase of ice-clouds and 

 frozen fogs, which have high reflective power, low specific heat, and 

 low diathermacy. 1 



5. A progressive reduction of the moisture in the air, and hence a 

 decrease of its blanketing effects. 



6. Some minor agencies that may be passed by. 

 These were opposed by the following: 



1. The giving forth of carbon dioxide from the ocean because of 

 the reduced pressure of the carbon dioxide of the air, as the latter was 

 consumed. 



2. A reduction of the contact area between land and air by the 

 growth of the ice-fields, and hence the checking of the carbonation of 

 the rocks. 



There was a residual effect arising from changes in the amounts of 

 vegetal growth, animal life, and organic decay, that was felt on the one 

 side or the other, but it is not easy to strike the balance. Probably, 

 the ratio of animal life to vegetal growth was rather higher than before, 

 as the carbon dioxide declined, as the relative amount of oxygen 

 increased, and as the cold increased; but decay was probably also 

 checked, and the formation of peat and similar residues of organic 

 matter promoted. On whichever side it may have fallen, the balance 

 was probably not very important. 



It will be noticed that these opposing agencies came into effect 

 only after the glaciating agencies had done such part of their work 

 as brought these opposing agencies into activity; and hence they 

 lagged behind the effects they tended to offset. For example, the 

 diffusion of carbon dioxide from the ocean to the air requires time. 

 Its effects could only be felt some time after those of the cause of 

 the diffusion. Besides, interchange between the main body of the 

 ocean and the air was especially retarded by the surface layer of fresh 

 uncarbonated water that came from the melting of sea-ice, and even 

 of the land-ice, and by the superficial layer especially affected by pelagic 

 life. 



The checking, at length, of the glacial acceleration, is assigned to 

 the following agencies, particularly the first: 



1. The completion of the higher carbonation of the ocean, followed 



1 The specific heat of ice is 0.504, that of water being unity. For diathermacy, 

 see Preston's Theory of Heat, pp. 466, 467, 1894. 



