54 



Anniversary Meeting. [Nov. 30, 



with great rapidity, and not in one spot only, and continued to do so 

 down to the present time. 



Lastly, the advent of the Miocene period, in the polar area, was 

 accompanied with the production of a profusion of genera, the majority 

 of which have existing representatives which must now be sought in a 

 latitude 40° farther south, and to which they were driven by the 

 advent and advance of the glacial cold ; and here Count Saporta's 

 conclusions accord with those of Professor A. Gray, who first showed, 

 now twenty years ago, that the representatives of the elements of the 

 United States Flora previously inhabited high northern latitudes, from 

 which they were driven south during the Glacial period. 



Perhaps the most novel idea in Count Saporta's Essay is that of the 

 diffused sunlight which (with a densely clouded atmosphere), the 

 author assumes to have been operative in reducing the contrast 

 between the polar summers and winters. If it be accepted it at 

 once disposes of the difficulty of admitting that evergreen trees 

 survived a long polar winter of total darkness, and a summer of con- 

 stant stimulation by bright sunlight ; and if, further, it is admitted 

 that it is to internal heat we may ascribe the tropical aspect of the 

 former vegetation of the polar region, then there is no necessity for 

 assuming that the solar system at those periods was in a warmer area 

 of stellar space, or that the position of the poles was altered, to account 

 for the high temperature of Pre- Glacial times in high northern 

 latitudes ; or, lastly, that the main features of the great continents 

 and oceans were very different in early geological times from what 

 they now are. Count Saporta's views in certain points coincide 

 with those of Professor Le Conte of California, who holds that the 

 uniformity of climates during earlier conditions of the globe is not 

 explicable by changes in the position of the poles, but is attributable 

 to a higher temperature of the whole globe, whether due to external or 

 internal causes, to the great amount of carbonic acid and water in the 

 atmosphere, which would shut in and accumulate the sun's heat, 

 according to the principles discovered by Tyndall and applied by 

 Sterry Hunt in explanations of geological times. Le Conte, however, 

 admits the possibility of the earth's having occupied a warmer position 

 in stellar space, of its having exhibited a more uniform distribution of 

 surface temperature, and a different distribution of land and water.* 



Before Count Saporta's Essay had reached this countryf another 

 contribution to the subject of the origin of existing Floras had been 

 communicated to our own Geographical Society, by Mr. Thiselton 

 Dyer, in a Lecture on " Plant Distribution as a field for Geographical 



* Professor Jos. Le Conte, in " Nature," October 24, 1878, p. 668. 



f Count Saporta's Essay was presented to the International Congress of Geo- 

 graphical Science which met in Paris in 1875, and was not received by me till the 

 autumn of 1878, though it bears the date 1877 on the title page. 



