330 J. LE CONTE — LAND-ELEVATION AND ICE-ACCUMULATION. 



raous, in consequence of the reluctant yielding of the crust and the capacity 

 of ice to reproduce the conditions of its own accumulation. Although the 

 elevation produced the cold and therefore the ice-accumulation, yet the latter 

 culminated long after the former had ceased and even after a contrary move- 

 ment had commenced. 



I have been accustomed to illustrate this view by the accompanying dia- 

 gram, figure 1. In this diagram, which, for simplicity's sake, treats the 

 glacial epoch as one, the horizontal line, A B, represents time from the later 

 Pliocene until now ; but it also represents the present condition of things 

 both as to land-level and as to ice-accumulation. The full line, c d e, repre- 

 sents the oscillations of land (and presumably of temperature) above and 



^Irocene 



GlaciaJ 



ChaSpl^^ 



Present 



Figure 1. — Graphic Representation of Quaternary Climate and Land-Altitude. 



below the present condition. The broken line represents the rise, culmi- 

 nation and decline of ice-accumulation. The dotted line represents the crust- 

 movement as it would have been if there had been no ice-accumulation. 



It is seen from the diagram that the ice-accumulation culminated at a time 

 when the land, under the pressure of the ice-load, had already commenced 

 to subside ; and that the subsidence was greatest at a time when the pressure 

 had already commenced to diminish. But the fact that the land, after the 

 removal of the ice-load, did not return again to its former height in the Pli- 

 ocene, is proof positive that there were other and more fundamental causes 

 of crust movement at work besides weighting and lightening. The land did 

 not again return to its former level because the cycle of elevation, whatever 

 its cause, which commenced in the Pliocene and culminated in the early 

 Quaternary, had exhausted itself If it had not been for the ice-load inter-\ 

 fering with and modifying the natural course of the crust movement deter- 

 mined previously and primarily by other and probably internal causes, the 

 latter would probably have taken the course represented by the dotted line. 

 It would have risen higher and culminated later, and its curve would have 

 been of simpler form. 



