72 ON FOSSIL PLANTS DISCOVERED IN GEINNELL LAND. 



remains were found, supposing the position of the earth to have 

 remained the same. 



Mr. Sollas remarked that Prof. Heer had already shown that the 

 Miocene flora diminished both in genera and species when traced 

 from Switzerland northward, in such a manner as to indicate that 

 while the temperature of the northern hemisphere was generally 

 higher in Miocene times, yet it decreased towards the north pole 

 very much as it does now, only more slowly. Capt. Feilden's 

 remarks on the thinning- out of species from Spitzbergen to Grinnell 

 Land were quite in accordance with this. It thus certainly appeared 

 to him that it was not the geographical position of the poles, but the 

 climatal conditions of the polar regions which had undergone a 

 change. As regards a higher temperature, Dr. Croll's theory would 

 account for that. As regards the necessity for light, it seemed to 

 him that a long winter merely meant for the arctic plants a longer 

 sleep. The light of a short summer would reach the ground unaf- 

 fected by the absorptive action of aqueous vapour, which would 

 filter out a good deal of the non-luminous heat-rays. In high 

 northern latitudes heated by warm currents of water, we should 

 have produced during the Miocene times natural conditions very 

 similar to those produced artificially in the greenhouse of St. Peters- 

 burg : aqueous vapours would furnish a very efficient substitute for 

 glass ; and oceanic currents would serve for a warming-apparatus. 



