166 Jame8 Geikie — On Changes of Climate. 



pensated for by the great summer heat and its marvellous effect on 

 vegetation, . .. , In both America and Siberia there is a zone of 

 debatable ground, in which the mammals of the Arctic and tem- 

 perate provinces are continually oscillating to and fro, according to 

 the seasons. And in this their skeletons could not fail to be mixed . 

 together in the deposits of the rivers." But before we decide that 

 the climate of England in " Pleistocene " times resembled that of 

 Siberia and North America at the present day, it is necessary to 

 ascertain whether the causes that induce the latter could possibly 

 have existed in Britain at a time when, as it is supposed, glaciers 

 still covered large areas in that country and Ireland. 



At Jakutsk (62° N. lat.) the temperature of January is— 43° 8' F., 

 while that of July is 62° 2' — truly a wonderful contrast ! The 

 eavises of the intense winter are not far to seek. During that season 

 every wind that blows across Siberia, no matter whence it comes, is 

 bitingly cold. The west winds that temper our winters with the 

 warmth of the Grulf-stream ar6 robbed of their moisture and cooled 

 down before they cross the snows of the Ural Mountains to pour 

 into Siberia. The gales from the Arctic Ocean are still colder, nor 

 is much warmth derived from the winds that sweep northwards from 

 the high Mongolian plateau. In summer-time the conditions are re- 

 versed. Dry and scorching winds reach Siberia from the west, and 

 the heat of the Mongolian deserts is wafted from the south ; while 

 at the same time the northern plains are warmed by the continuous 

 shining of the Arctic sun ; and thus the temperature rises rapidly all 

 over Siberia. In North America the seasons are also more marked 

 than with us, and the causes for this are somewhat similar to those 

 which induce the more strongly contrasted summers and winters of 

 Northern Asia. 



If we could obliterate the German Ocean and the English Channel, 

 would this change bring about summers and winters as well marked 

 as those that characterize the higher latitudes of Asia and America ? 

 Surely not, for so long as our western shores continued to be washed 

 by the Atlantic, our climate would necessarily partake of an "insular" 

 character. The summers would possibly be a little warmer, and the 

 winters a little colder, but there is nothing to justify the supposition 

 that the seasons would at all resemble those of Siberia or the inland 

 parts of North America. But the migrations of the Arctic and 

 southern fauna are thought to have taken place at a time when snow- 

 fields and glaciers were nourished in the uj)land districts of Great 

 Britain. The mere presence of perennial snow and ice, however, 

 eould not possibly bestow a Siberian climate on England. With 

 Scotland and the hilly districts of England and Ireland buried 

 underneath snow and ice, we may reasonably infer that the glaciers 

 of Switzerland must have greatly exceeded their present dimensions ; 

 that the mountains of the Vosges and the Black Forest would have 

 their permanent snow-fields ; and that Scandinavia would be in a 

 truly glacial condition. In short, the winters of Eixrope would then 

 necessarily be very much colder than they are now : and it follows 

 from this that the summer temperature would also be greatly lower 

 than at present. For if we conceive that the prevalent winds in 



