COSMIC PHILOSOPHY 



have taken place during millions of years gone 

 by or which are sure to take place during mil- 

 lions of years to come, on the other hand we 

 are not yet able to assign an approximate date 

 for the most recent epoch at which our north- 

 ern hemisphere was covered with glaciers. Ac- 

 cording to Mr. Wallace this epoch may have 

 occurred no more than seventy thousand years 

 ago, while others would assign to it an antiquity 

 of at least two hundred thousand years, and 

 there are yet others who urge strong arguments 

 in behalf of the opinion that a million of years 

 is barely enough to have produced the changes 

 which have taken place since that event. Nev- 

 ertheless, though we cannot determine the 

 amounts and durations of the movements which 

 have occurred during the geologic history of 

 the earth, we can still securely assert that these 

 movements have been rhythmical in character. 

 Though the verdict is rendered with less pre- 

 cision, its purport is still the same. In the 

 alternating periods of elevation and depression 

 which have succeeded each other at different 

 places ever since the earth's crust began to be 

 solidified, are exemplified the chief geologic 

 rhythms, due to the slow deflection of the lines 

 of least resistance along which the pressure of 

 the earth's nucleus reveals itself by causing 

 upward motion. But these immensely long 

 rhythms are complicated by minor rhythmical 

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