66 Prof. O. Heer on the Miocene Flora 



beautiful and varied fossil plants which fill the rocks of Atane- 

 verdlak in Greenland, will be convinced that these plants can- 

 not have come from a great distance. As to the fossil plants 

 of Spitzbergen, it is very evident that they were not brought 

 by marine currents, as we find them in freshwater deposits. 



It appears certain, therefore, that at the Miocene epoch the 

 temperature of the polar regions was much higher than in 

 our day ; and we are naturally led to inquire what are the 

 causes which may have brought about such a change. We 

 cannot admit the supposition of a displacement of the poles, 

 even regarding it in the same way as Mr. Evans, who has re- 

 cently maintained this theory. Indeed it is a certain fact that 

 we remark the same phenomena all round the terrestrial globe, 

 not only in the polar zone, but also under southern latitudes. 

 No direct observation seems to us to confirm this hypothesis. 

 We regard as much more important the theory according to 

 which climatic modifications would coincide with modifica- 

 tions in the distribution of the seas and continents upon the 

 surface of the globe. At present the extent of the seas is 

 twice and a half that of the solid earth, and the continents are 

 arranged in much more considerable masses in the northern 

 hemisphere, and especially beyond the tropic. This condition 

 is not normal. If, instead of so unequal a distribution, the 

 lands and seas were equally distributed in all the zones, the 

 temperate and glacial zones would enjoy a climate warmer 

 than at present. Nevertheless, even supposing the most 

 favourable distribution, we should not succeed in producing, 

 between 70"^ and 79° N. latitude, a temperature sufficient for 

 the development of a flora like that of which the existence 

 in these regions during the Miocene period has just been in- 

 dicated. Suppose all the continents united in the neighbour- 

 hood of the equator, and only a few islands left in the northern 

 regions, — these would enjoy the highest mean temperature to 

 which they could attain, their winters would be compara- 

 tively very mild, and yet the heat of the sun could not be suf- 

 ficient between 70" and 80° N. lat. to allow of the development 

 of a vegetation so rich as that of which we find the traces. 

 Now it is certain that in the Miocene period there was a great 

 extent of solid land in the temperate zone, and even in the 

 polar regions, as is proved to us by the extension of several 

 species of the Miocene flora, which we can follow from the 

 Mackenzie to Spitzbei'gen. 



The explanation of the climatic changes which the study of 

 fossils reveals to us, has been sought in the fact that the 

 gradual cooling of the mass of the globe must necessarily pro- 

 duce a gradual diminution of temperature. This cause may 

 certainly have acted in the most ancient periods ; but the Mio- 



