104 UNIFORMITY OF CLIMATE IN PAST AGES. 



heat-transparency was proportional to the decrements. 

 Hence, one would expect a more rapid fall of tempera- 

 ture in the later than in the early geological periods. 

 This is in accord with the facts. The change was very 

 slow during the first half of the geological time, a little 

 more rapid during the next portion, — the mesozoic — 

 more rapid in the tertiary, increasing yet more through 

 its latter part, till, at last, the air becoming probably as 

 pure as now, polar regions ceased to be inhabitable, 

 snow and ice accumulated under the action of a sun that 

 never rose above the horizon at the poles, and, in 

 present temperate latitudes, rose only to its present 

 height at the equinoxes. Under such conditions, aided 

 by high latitude uplifts, it seems not difficult to under- 

 stand why that time of cold known as the glacial epoch 

 set in, and that it would have continued to the present 

 day had the axis remained perpendicular to the ecliptic 

 and the land retained its elevation. Furthermore, we 

 know that the land in high latitudes was depressed after 

 that until it was much lower than now — sufficiently so 

 to submerge a very large part of what is at present dry 

 land. The effect of this was to hasten the departure of 

 the ice and to soften the climate, making it even warmer 

 than it is now. When the land rose to its present eleva- 

 tion, present temperature set in. 



It is believed that this theory, in its entirety, pos- 

 sesses the merit of novelty, whatever that may be. It 

 may be summed up in a few words. The warmth of pre- 

 glacial climate was due chiefly to the large amount of 

 CO 2 and aqueous vapor in the atmosphere. The even- 

 ness of temperature and the uniformity in those bio- 

 logical conditions which depend upon actinic influences 

 were due to the axis being perpendicular. The cold of 

 the glacial epoch was due to the loss of CO 2 and aqueous 

 vapor, and to the perpendicularity of the axis aided by 

 high latitude uplifts. The warmth of the Champlain 



56 



