556 F. H. KyOWLTOX EVOLUTIOX OF GEOLOGIC CLIMATES 



Antarctic table-land, 9.000 feet above sealevel, the ice is dwindling and 

 the glaciers retreating. In this area, at least, depression might extend 

 giaciation by increasing precipitation. 



If it were worth while, an indefinite nnmber of quotations both for 

 and against this elevation hypothesis could be made; but out of this 

 wealth of more or less conflicting t-estimony, it seems to me there must 

 come the conviction that it may nevertheless have played a relatively 

 important, though not always the major, role in the production of giacia- 

 tion. We know that even under the present system of solar control of 

 temperatures, if there is given the recjuisite elevation and adec^uate pre- 

 cipitation, accumulation of snow and ice will result. It might even be 

 possible on this basis to explain a majority of the evidences of giaciation 

 that have been described from the earlier rocks: for, as already men- 

 tioned, they are or may be of the well known mountain type of giaciation. 

 But it seems to me improbable, not to say impossible, with the atmosphere 

 controlled by the sun, for elevation alone to account for the inauguration 

 of the three major periods of glacial activity. The Pleistocene giaciation 

 was most extensive in Xorth America. It was laid down over a broad, 

 fairly level plain, and to my mind there is no convincing evidence of a 

 continental elevation that seems adec[uate to account for its initiation. 

 Still less does it seem competent to account for the "Permo-Carbonifer- 

 ous'' giaciation. As has been shown, however, even a moderate elevation 

 coupled with non-solar control seems fully competent to explain all type? 

 of giaciation. 



Changes in atmosplienc circulation hypothesis. — This explanation^ 

 which was especially advocated by Harmer^^ as applied to the Pleistocene 

 climate of northwestern Europe, is conditioned on changes in atmospheric 

 circulation resulting from geographic changes such as variation in conti- 

 nental outline and elevation. It is, of course, well known that quite 

 marked meteorological phenomena are dependent on or influenced by 

 terrestrial config-uration, but this hypothesis fails utterly to explain the 

 initiation of the equatorial ^Termo-Carboniferous*' giaciation, or of trop- 

 ical or semitropical temperatures in polar lands. Moreover, atmospheric 

 circulation, as here made use of, is of necessity based on the assumption, 

 not considered tenable by the writer, that the sun has controlled earth 

 atmosphere throughout the whole of geologic time as it does now. That 

 this was a minor contributing factor during Pleistocene and subsequent 

 time is possible, but it could hardly have been more than this when vre 

 reach the points at which the giaciation took place — some on mountains,. 



F. W. Harmer : Jour. Geol. Soc, vol. 57, 1898, pp. 405-472. 



