Page:Quarterly Journal of the Geological Society of London, vol. 34.djvu/106

72 remains were found, supposing the position of the earth to have remained the same.

Mr. 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 unaffected 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. Petersburg: aqueous vapours would furnish a very efficient substitute for glass; and oceanic currents would serve for a warming-apparatus.