Date of the Glacial and the Upper Miocene Period. 383 



In the discussion of the subject of geological climate another 

 point has been greatly overlooked, viz. the enormous influence 

 that a mantle of ice continually lying on the continent of Green- 

 land has upon the climate of the northern hemisphere. If we 

 could by some means or other remove this cold mantle off that 

 continent, though all things else should remain the same, the 

 effect that its simple removal would have on the climate of the 

 entire northern hemisphere would be quite magical. On a former 

 occasion we referred to the physical reason of this, but shall have 

 occasion to return again to this part of the question. 



In looking over Table I., which, as has already been remarked, 

 probably embraces the greater portion of the Tertiary age, the 

 excentricity several times attained pretty high values, although 

 it is only at the three periods embraced in Tables II., III., and IV. 

 that the values reached would be likely to lead to a condition of 

 things during the past three millions of years that might be pro- 

 perly designated a glacial epoch. But as the excentricity during 

 the greater part of that vast period was greater than it is at 

 the present day (for we are just now much nearer to the infe- 

 rior limit than we are to the superior limit), its effect on climate 

 would be more marked than it is at present. The effect would 

 be that, as a general rule, during the greater portion of the 

 three millions of years past, the climate would be somewhat 

 colder when the winters occurred in the aphelion than it is at the 

 present day, and a good deal warmer when they occurred in the 

 perihelion than at present. 



Judging from geological evidence alone, we naturally con- 

 clude that, as a general rule, the climate of the Tertiary period 

 was somewhat warmer than it is at the present day. It is from 

 fossil remains that the geologist principally forms his estimate 

 of the character of the climate during any period. Now, in re- 

 gard to fossil remains, the warm periods will always be far better 

 represented than the cold ; for we find that, as & general rule, those 

 formations which geologists are inclined to believe indicate a cold 

 condition of climate are remarkably devoid of fossil remains. If a 

 geologist does not keep this principle in view, he will be very 

 apt to form a wrong estimate of the general character of the 

 climate of a period of such enormous length as the Tertiary. 



Suppose that the presently existing sea-bottoms, which have 

 been forming since the commencement of the glacial epoch, were 

 to become consolidated into rock and then elevated into dry land, 

 we should then have a formation which might be properly de- 

 signated the Postpliocene. It would represent the time which 

 has elapsed from the beginning of the glacial epoch to the pre- 

 sent day. Suppose one to be called upon as a geologist to' 

 determine from that formation what was the general character 



