ScuAiM'F — Forme)' Li/ml-Bruh/e hcltveen N. Fjuvopc dtid N. Ainrricn. -j 



The remarkable circuniHtaiico thai Ihe siibiiiarinc tjord-valliiyH on the 

 European and on the American .side, and likcwiHe the Hiibmarine ridges 

 connecting the two continents, are situated at about the same deptli makes it 

 probable that the whole area luul once been raised simultaneously, and had thus 

 become connected by land. This was not Dr. Nansen's opinion only (p. 1 7."). 

 Professor Dana long ago urged that tlie refrigeration of the climate at the 

 close of the Tertiary era was connected with a period of high-latitude elevation.' 

 Dr. Wright and Mr. Uphani, tw(j well-known American authorities on glacial 

 phenomena, expressed the view that the northern lands must have been 

 gradually elevated in Pliocene times, becoming continuous before the Ice Age.^ 

 They assume that North America thus became joined to northern Asia 

 across the area of the shallow Bering Sea, while land extended from Norway 

 to the Faroes, Iceland, and Greenland. 



Incidentally Dr. Wright warns \is that a cautious attitude of agnosticism 

 with re.spect to the cause of the Glacial period is most scientific and becoming. 

 Nevertheless I venture to think, and cannot refrain from expressing my 

 opinion, that the Glacial period was primarily due to the diversion of 

 oceanic currents produced by changes in the distiibution of land and water. 

 This again is no new suggestion. It was put forward, among others, by 

 Dr. Wallace,' and has, I believe, been adopted by many naturalists. With 

 every respect for the views of those who hold difl'erent opinions, it seems 

 to me that the peculiar phenomena connected with the Ice Age in western 

 Europe, and especially the apparent survival of southern species of plants 

 and animals in Ireland through the Glacial period, are best explained by 

 such a theory as that just stated. No doubt astronomical causes, as Sir 

 lioljert Ball has so clearly demonstrated, have afl'eeted the temperature of 

 the northern liemi.sphere conjointly.* However, as it is not my intention 

 to engage in the speculative discussion of the causes of the Ice Age, I nuiy 

 as well turn to the biogeographical evidences for the former existence of a 

 North Atlantic land-bridge. 



It is especially the teachings of Edward Forbes and A. E. Wallace that 

 led to the recognition of the significance of the present geographical distri- 

 bution of animals and plants as an indicator of the changes which have taken 

 place in the arrangement of land and water. They believed that many terres- 

 trial animals and plants require a continuous land-surface for tlieir dispersal. 



' Dana, J. D., "Manual of Geology," 3rd edition, p. 'i-lO. 



• Wriglii, F., and W. Upliam, " Greenland Itefields," p. 331. 

 3 Wallace, A. R., " Island Life," pp. luO-161. 



* Ball, R., " The Cause of an Ice Age." 



