THE CAUSE OF THE GLACIAL PERIOD. 497 



Upham, in the appendix to the original edition of this volume 

 and his conclusions have been supported by so many lines of 

 evidence which have since come to light, that we now insert 

 it in the body of the discussion with such supplementary 

 notes as he has thought it necessary to add. It is a signifi- 

 cant confirmation of his views that Professor Chamberlin's 

 theory of the effect of the diminution of the carbonic dioxide 

 in the atmosphere in producing glacial conditions involves 

 extensive continental elevation of land surfaces as prelimi- 

 nary to the supposed depletion of this important element. 



An examination of the evidence of changes in the relative 

 heights of land and sea in various parts of the world during 

 Quaternary time has led me to an explanation of the causes of 

 theGlacial period, which, in this application of its fundamental 

 principle, seems to be new, while in its secondary elements 

 it combines many of the features of the explanations proposed 

 by Lyell and Dana and by Croll. Briefly stated, the condi- 

 tion and relation of the earth's crust and interior appear to be 

 such that they produce, in connection with contraction of the 

 earth's mass, depressions and uplifts of extensive areas, some 

 of which have been raised to heights where their precipita- 

 tion of moisture throughout the year was almost wholly 

 snow, gradually forming thick ice-sheets; but under the heavy 

 load of ice subsidence ensued, with correlative uplift of other 

 portions of the earth's crust; so that glacial conditions may 

 have prevailed alternately in the northern and southern hemis- 

 pheres, or in North America and Europe, and may have been 

 repeated after warm interglacial epochs. 



Quaternary oscillations of land and sea in glaciated regions 

 have been discussed by Croll and Geikie on the assumption 

 that the earth was so rigid that its form would not be changed 

 by the load of the ice-sheet nor by its removal, which seemed 

 more probable because of the well-known physical and mathe- 

 matical researches of Hopkins, Thomson, Pratt, and Professor 

 G. H. Darwin, who conclude that the earth is probably solid, 



