no EVOLUTION OF THE EARTH 



single cause of the last or Pleistocene glacial period is the 

 great continental elevation which formed the Cascadian revo- 

 lution, but, so far as our knowledge goes, that would not 

 account for the successive advances and retreats of the ice 

 mantle, with the attendant climatic variation, and some other 

 factor such as the rhythms of solar energy must be invoked as 

 of supplemental influence. Nevertheless, the ultimate source 

 of profound and far-reaching crises in the evolution of the 

 organic world may have been, geologically speaking, of a very 

 simple character. 



Through the collaboration of my colleagues. Professors 

 Schuchert and Barrell, the appended chart. Figure 14, has 

 been prepared to show the relation between the changing con- 

 tinental elevation and climate. To this I have added a curve 

 representing the consequent acceleration and retardation of 

 the evolutionary stream. The climatic records of pre-Paleo- 

 zoic time are so vague and unreliable that it was not thought 

 wise to include the vast Archeozoic and Proterozoic eras 

 within the scheme. The time values of the several included 

 eras are not proportionally indicated, too much, space by far 

 being given to the Cenozoic because of its biologic interest. 

 As a matter of fact, its duration is more nearly comparable 

 to that of Permian time. 



The curves are necessarily generalized, for there was 

 neither space nor necessity for greater detail. In the altitu- 

 dinal curve, the upslope of the diastrophic peaks signifies 

 rising diastrophism; the downslope, the period of erosion 

 before the continents are low enough to have mantles of sedi- 

 ment spread upon them. A greater or lesser part of the peak 

 and downslope represents, therefore, the unrecorded interval 

 between eras or periods, as the case may be. The tangential 

 lines drawn to the diastrophic peaks show the relation of a 

 series of movements: a gradual rise culminating in the great 

 revolutions. Were the Cenozoic compressed into its normal 



