of Secular Changes of Climate. 91 



5. Mr. Wallace admits, of course, that the necessary geo- 

 graphical conditions existed during the glacial epoch ; for, 

 unless this had been the case, no glacial epoch could have oc- 

 curred. Therefore all that was required to produce glaciation 

 was an amount of eccentricity sufficient to set the physical 

 agencies into operation. Be it observed, it did not require, in 

 addition to the physical agencies, some changes in the geo- 

 graphical conditions, or some new conditions ; for the geogra- 

 phical conditions being existent, all that was then required to 

 bring about the glacial epoch was the operation of the physical 

 agencies. The overlooking of this fact has led to much con- 

 fusion. For example, 210,000 years ago, with winter in 

 aphelion, "the problem to be solved," says Mr. Wallace, 

 u is, whether the snow that fell in winter would accumulate to 

 such an extent that it would not be melted in summer, and 

 so go on increasing year by year till it covered the whole of 

 Scotland, Ireland, and Wales, and much of England. Dr. 

 Croll and Dr. Greikie answer without hesitation that it woulcl. 

 Sir Charles Lyell maintained that it would only do so when 

 geographical conditions were favourable " (p. 136). Here 

 we have a complete misapprehension of the relation between 

 Sir Charles LyellV views and mine; for I would certainly 

 maintain (and, I presume, Dr. Greikie also) as emphatically 

 as Sir Charles could do, " that it would only do so when 

 geographical conditions were favourable." For undoubtedly, 

 according to the theory advocated in c Climate and Time,' no 

 glacial epoch could result without geographical conditions 

 suitable for the operation of the physical agencies ; and this 

 is virtually what Sir Charles maintains. The glacial epoch 

 resulted during the last period of high eccentricity because 

 the geographical conditions suitable for the effective operation 

 of the physical causes then existed. 



6. It is assumed in c Climate and Time ' that, with the excep- 

 tion of those resulting from oscillations of sea-level, afterwards 

 to be considered, the general distribution of sea and land, 

 and other geographical conditions, were the same during the 

 glacial epoch as they are at present*. Consequently, in ac- 

 counting for the glacial epoch I had only to consider the 



* Prof. J. Geikie, however, believes that during early Postglacial times 

 a considerable change in the physical geography of the North seas took 

 place (see ( Prehistoric Europe/" chap. xxi.). In order to account for the 

 floras of Greenland, Iceland, and the Faroe islands, he thinks a land 

 connexion must have existed between these places and Scandinavia. For 

 reasons which will be stated on a future occasion I am somewhat doubtful 

 on this point. There is, I think, an important agent overlooked in 

 the question of the distribution of Arctic flora and fauna. Prof. Geikie, 

 however, does not believe that the climatic condition of that period was 

 in any way due to this change. 



