of Secular Changes of Climate. 373 



for any theory of eccentricity in accounting for the Glacial 

 Epoch. 



If we adopt the Physical theory of the cause of the Glacial 

 Epoch, we are compelled to maintain that the last two great Ice- 

 periods were the indirect results of a high state of eccentricity, 

 and in this case we can hardly avoid the conclusion that the 

 mild intervening period was due to the same cause. The 

 occurrence of a mild interglacial period between the two ice- 

 periods is directly in opposition to Mr. Wallace's view — that 

 during a high state of eccentricity the ice would not disappear 

 but be continued. It is in perfect harmony, however, with 

 that which I advocate ; for during high eccentricity a mild 

 and equable condition of climate, when the winters occur in 

 perihelion, is as much a necessary result as a cold and glacial 

 condition when they occur in aphelion. 



The facts of Geology thus to me appear so far to be as much 

 opposed to Mr. Wallace's modifications as are the principles 

 of Physics. 



Difficulty in detecting the Climatic Character of the earlier 

 Interglacial Periods. — It follows according to theory that, other 

 things being equal, the greater the amount of eccentricity the 

 more equable and mild will the interglacial periods be. It is 

 probable therefore that some of the earlier interglacial periods 

 were milder and more equable than the last. It may be difficult 

 in the present state of our knowledge to prove this conclusion 

 by direct geological and palseontological evidence ; but, on 

 the other hand, it is certainly impossible to disprove it by that 

 means. The absence of deposits containing organic remains 

 indicative of a superior mildness of climate having obtained 

 during early interglacial periods cannot certainly be regarded 

 as satisfactory evidence against the conclusion just referred to. 

 When we consider the enormous pressure and destructive 

 power of an ice-sheet some 2000 or 3000 feet in thickness 

 grinding down the face of a country, our surprise is that so 

 much evidence remains of even the last interglacial period. 

 That so few relics of the flora and fauna of preceding inter- 

 glacial periods have been preserved is a conclusion which we 

 might a priori anticipate. This fact has been clearly pointed 

 out by Mr. Wallace himself, who says : — " If there have been, 

 not two only, but a series of such alternations of climate, we 

 could not possibly expect to find more than the most slender 

 indications of them, because each succeeding ice-sheet would 

 necessarily grind down or otherwise destroy much of the 

 superficial deposits left by its predecessors, while the torrents 

 that must always have accompanied the melting of these huge 

 masses of ice would wash away even such fragments as might 

 have escaped the ice itself" (p. 118). 



