H 



meteoric matter, circulating near the sun, as this hypothesis 

 would require, appears to be inconsistent with what we know 

 of the equilibrium of the solar system. 



Moreover, it does not appear at all probable that a colder sun 

 would produce a glacial climate. The chief requisite for the 

 production of glaciers, and consequently of icebergs, which are 

 floating fragments of the vast Polar glaciers, is the fall of snow; 

 the snow-bearing clouds are fed by evaporation, and evaporation 

 requires solar heat ; so that, as Tyndall has expressed it, dimi- 

 nution of the sun's heat would cut off the glaciers at the source. 

 We may no doubt imagine such cold as would freeze the oceans 

 to a distance of forty-five degrees of latitude round each pole, 

 but this would not account for rocks scratched by glaciers and 

 boulders borne by icebergs, for these show the icebergs and 

 glaciers to have been in motion. 



On the other hand, the fact of the climate of, at least, the 

 higher and middle latitudes having been formerly much warmer 

 than at present, may be reasonably accounted for by supposing 

 that the sun was then hotter than now ; and this is not only 

 an admissible supposition, but appears to be necessarily true ; 

 because a body which is constantly emitting heat must in the 

 course of time grow cooler, unless it receives supplies of heat or 

 of fuel from without ; and in the case of the sun this appears 

 impossible, except to a comparatively small extent, through the 

 in-falling of meteors. Heat is probably being produced by the 

 subsidence, or falling in, of his surface, but no action of this 

 kind can sustain the temperature at the same level for an 

 indefinite time. 



If "the imperfection of the geological record "* permits it, 

 we ought to expect to find evidence of a progressive cooling ; 

 and the fossil flora of the Arctic regions does seem to yield 

 such evidence. On this subject we have abundant information 

 from the discoveries of Professor Nordenskiold, who has probably 

 done more than all other explorers put together to increase 

 our knowledge of Arctic geology, and from the researches 

 of Professor Heer of Zurich on the fossils brought home 



* This is Darwin's expression, bein^ the title of a chapter of his Origin of Sptciet. 



