CAUSE OF MILD POLAR CLIMATES. 165 



climate, that because the eccentricity may have been 

 high at some particular period there must necessarily 

 have been a glacial epoch. The erroneous nature of 

 this misapprehension of the theory has already been 

 shown at considerable length in Chapter V. Eccen- 

 tricity can produce glaciation only through means of 

 physical agencies, and for the operation of these 

 agencies a certain geographical condition of things is 

 absolutely necessary. We know with certainty that 

 during the Tertiary period the eccentricity was at 

 times exceptionally high, as, for example, 2,500,000 

 and 850,000 years ago ; but whether a glacial epoch 

 occurred at these periods depended, of course, upon 

 whether or not the necessary geographical conditions 

 then obtained. Supposing the necessary geographical 

 conditions for glaciation did exist at the two periods 

 in question, still if these conditions differed very much 

 from those which now obtain, the glacial state of 

 things then produced would certainly differ from that 

 of the last glacial epoch. This is obvious, for the same 

 physical agencies acting under very different conditions 

 would not produce the same effects. Under almost 

 any geographical condition of things eccentricity would 

 produce marked effects, but the effects produced might 

 not amount to glaciation. In the Tertiary age, during 

 high eccentricity, the effects resulting might possibly 

 have been as well marked as they were during the 

 Glacial Epoch ; but these effects must have differed 

 very much from those produced at that epoch. We 

 have seen that, owing to that peculiar geographical 

 condition of things existing during the Tertiary period, 

 the physical agents brought into operation by a high 

 state of eccentricity would have a much greater 

 influence in raising the temperature of the northern 

 hemisphere when the winters occurred in perihelion, 



