3 66 THE POPULAR SCIENCE MONTHLY. 



not be necessary to go far to the north to meet perpetual snow. For 

 snow once fallen, or ice once formed, would never melt, but, accumu- 

 lating through the ages, would force its way by its own weight equa- 

 torward until it reached a region where the heat of the sun was suffi- 

 cient to melt it away. The uplifts in high latitudes intensified the 

 results. Vice versa, when the axis became oblique, more solar heat 

 fell within the polar circle, those regions became warmer, and the Gla- 

 cial epoch departed. If these conditions a perpendicular axis and 

 high uplifts could be to-day restored, the atmosphere remaining as it 

 is, the Glacial epoch would return. 



The removal of the ice was hastened by the depression of high- 

 latitude lands. This depression was very extensive. Vast tracts were 

 submerged. In this is found, I think, the cause of the mild climate of 

 the Champlain, while the cold (the minor Glacial epoch) that followed 

 was due to another upward movement, or movements, comparatively 

 limited in extent in fact, confined mostly to Europe and Asia. 



Subsequent changes left us the climate of to-day. 



In the briefest possible space, I sum up as follows : 



The uniformity of plant-life, regardless of latitude, to near the 

 close of the Tertiary, indicates uniformity of biological conditions 

 i. e., of light, or actinic force, and heat. 



The former indicates that the earth's axis was approximately per- 

 pendicular a conclusion in harmony with the belief that the moon and 

 earth were once one body, and consequently that their axes were 

 originally parallel. 



The uniformity of temperature in high latitudes through the year 

 is also accounted for by a perpendicular axis, and, so far as I can see, 

 only by that. 



Astronomy tells only of present conditions. As to how or when 

 the axis took its present obliquity, it is unable to say. 



Geology fixes the date by the record which solar influences have 

 left on organic forms, and places it near or just after the close of the 

 Tertiary. 



The warmth of arctic regions for there might have been uniform- 

 ity without warmth was due to the " double blanket " of carbonic 

 acid and aqueous vapor. 



The cold of the Glacial epoch was due to the loss of CO 2 and aque- 

 ous vapor, aided by high-latitude uplifts. 



The disappearance of the ice and cold was due to the earth's axis 

 being made to incline as now, and to the reduction of the uplifts. 



The warmth of the Champlain was due to depression of the land. 



The second or minor ice period was due to another uplift confined 

 to (or at least much greater in) Europe and Asia. 



The depression of the land to somewhat near the present level, with 

 present amount of CO 2 and H 2 in the atmosphere, resulted in present 

 climatic conditions. 



