1878.J 



Presidents A ddress. 



53 



tion may be approximately drawn, its northern mnst have extended to 

 the Pole itself. 



I pass over Saporta's speculations regarding the initial condi- 

 tions of terrestrial life, which followed upon the emergence of the 

 earlier stratified rocks from the Polar Ocean, and proceed to his dis- 

 cussion of the climate of the carboniferous epoch as indicated by the 

 characters of its vegetation, and of the conditions under which alone 

 he conceives this can have nourished in latitudes now continuously 

 deprived of solar light throughout many months of the year. In the 

 first place, he accepts Heer's conclusions (founded on the presence of 

 a tree-fern in the coal measures specifically similar to an existing 

 tropical one), that the climate was warm, moisb, and equable, and 

 continuously so over the whole globe, without distinction of latitude. 

 This leads him to ask whether, when the polar regions were inhabited 

 by the same species as Europe itself, they could have been exposed to 

 conditions which turned their summers into a day of many months' 

 duration, and their winters into a night of proportional length ? 



A temperature so equable throughout the year as to favour a rich 

 growth of Cryptogamic plants, appears, he says, to be at first sight 

 incompatible with such alternating conditions as a winter of one long 

 night and a summer of one long day ; but equability, even in high 

 latitudes, may be produced by the effect of fogs due to southerly 

 warm oceanic currents, such as bathe, the Orkneys and even Bear 

 Island (in lat. 75° N.), and render their summers cool and winters 

 mild. To the direct effects of these he would add the action of such 

 fogs in obstructing terrestrial radiation, and hence preventing the evil 

 effects which its cold would otherwise induce ; and he would further 

 efface the existing conditions of a long winter darkness by the hypo- 

 thesis that the solar light was not, during the formation of the coal, 

 distributed over the globe as it now is, but was far more diffusive, the 

 solar body not having yet arrived at its present state of condensation. 



That the polar area was the centre of origination for the successive 

 phases of vegetation that have appeared in the globe is evidenced, 

 under Count Saporta's view, by the fact that all formations, Car- 

 boniferous, Jurassic, Cretaceous, and Tertiary, are alike abundantly 

 represented in the rocks of that area, and that, in each case, their 

 constitutents closely resemble that of much lower latitudes. The 

 first indications of the climate cooling in these regions is afforded by 

 Goniferce, which appear in the polar lower Cretaceous formations. 

 These are followed by the first appearance of Dicotyledons with 

 deciduous leaves, which again marks the period when the summer 

 and winter season first became strongly contrasted. The introduction 

 of these (deciduous-leaved trees) he regards as the greatest revolution 

 in vegetation that the world has seen ; and he conceives that once 

 evolved they increased, both in multiplicity and in diversity of form, 



