496 THE ICE AGE IN NORTH AMERICA. 



It is profitable, also, in this connection, to reflect on how 

 delicately balanced the forces of Nature now are with respect 

 to the production of glaciers. As already noted,* the gla- 

 ciers existing at the present time in the Alps have their peri- 

 ods of advance and recession. A slight increase in the 

 present snow-fall of Switzerland, if long continued, would 

 produce alarming results. From this cause alone, the 

 glaciers would at once begin to enlarge; and, in sympathy, 

 the temperature would fall, and the increase of the glaciated 

 area of Switzerland would go on until the whole country was 

 again brought under the desolating reign of ice, or until the 

 intervention of some counteracting force should stay its 

 advance. It is not without reason, therefore, that some 

 alarm was occasioned in Switzerland a few years ago by the 

 proposition to inundate the Desert of Sahara. Fortunately, 

 no extensive inundation of that region is within the reach of 

 human power. But, if it could be inundated, thus extend- 

 ing greatly the evaporating area from which the clouds 

 gather moisture for the Alpine heights, there is no telling 

 what the result might not be. Should there be an annual 

 increase of a foot of snow upon the Alps, a thousand addi- 

 tional feet of snow would have to be dissolved every thou- 

 sand years, with the enormous absorption of heat accom- 

 panying the process. This simple calculation is sufficient to 

 show the reality of the cause introduced by the eighth hy- 

 pothesis, which would explain the Glacial period through 

 the influence upon climate of changes in the distribution of 

 land and water. This cause is so effective that it may even 

 be conceived to be sufficient, without the introduction of any 

 other agencies. 



The ninth theory, which introduces considerable change 

 of levels ,n the continents, rests, without doubt, upon a true 

 cause, which, very likely, has cooperated with others, and 

 may in itself have been the chief agency in producing the 

 glacial conditions which we are studying. The evidence in 

 support of this theory was so well presented by Dr. Warren 



•See page 105. 



