THE CAUSE OF THE GLACIAL PERIOD. 521 



ordinary meteorologic conditions of high land elevation were 

 reinforced, in their tendency to produce ice-sheets, by the 

 concomitant depletion of atmospheric carbon dioxide. Now, 

 through the fruitful studies of Arrhenius, Chamberlin, and 

 others, we see how the great altitude of the Continents at 

 these two periods of great areas of long continued glaciation, 

 so very widely separated in time and therefore remarkably 

 unique and exceptional, worked in two ways, not only by 

 the common meteorologic effects, but also by the newly 

 recognized results of depletion of carbon dioxide, to give the 

 marvelous glacial periods thus ending Paleozoic and Ceno- 

 zoic time. 



Further studies will give the proportional effectiveness 

 of these two ways by which great uplifts of the continental 

 areas have induced glaciation. The final theory will rest 

 not less on the sagacious early views of Dana, with their 

 further advocacy by Le Conte and other writers, including 

 Wright and myself, than on the very helpful work of Arrhen- 

 ius and Chamberlin in their added contribution to explain 

 how the land uplifts accumulated ice-sheets with snowfall 

 all the year upon their vast expanses. Indeed I yet think, 

 that the broad view of the causation of glacial periods as 

 given above was presented truly and vividly, with no more 

 than the proper emphasis onthcvery exceptional occurrences 

 of only these two periods of general continental glaciation. 



Coming next to the great question whether the Pleistocene 

 ice-sheets of North America and Europe were wholly melted 

 away, as is argued by Professor James Geikie and less decid- 

 edly by Chamberlin and others, we cannot adduce sure 

 proofs for such conclusions from the central areas of these 

 great ice-sheets on the opposite sides of the Atlantic ocean. 

 The interior of New England and of British America, like 

 the central parts of Sweden and Norway, have not yet 

 revealed such sequence of glacial deposits and intervening 

 fossiliferous beds, of somewhat temperate faunas and floras, 



