10 



(b) That a planet whose internal heat has been prac- 

 tically exhausted, and which holds water and an at- 

 mosphere within the sphere of its control must reflect 

 solar energy deficient in those rays which are most 

 readily trapped, or selectively absorbed by its atmos- 

 phere, and it must have a low albedo, and that the color 

 of its reflected rays must be controlled by those least 

 readily utilized and trapped. 



(c) That glacial conditions may exist locally during 

 any period of a planet's climatic evolution provided 

 there be regions sufficiently elevated; but that an Ice 

 Age occurs as its oceans are finally exhausted of their 

 available remnant of planetary heat, that this age marks 

 the period during which surface temperatures pass from 

 interior to exterior control, or is the transition period 

 of its climatic evolution, and is unique. 



(d) There are two great eras in the climatic evolu- 

 tion of a planet: 1st, the era during which its internal 

 heat controls its surface temperatures, and solar heat 

 acts principally as a conservator of interior heat; 2nd, 

 the era of solar control of climates. The former being 

 an era of gradually decreasing temperatures, of uniform 

 distribution at sea level; and the latter an era of grad- 

 ually rising temperatures of a zonal distribution. The 

 two eras, so far as land areas are concerned, must be 

 separated by an Ice Age. The difference in the specific 

 heat of land, and that of water, permits the land areas 

 to cool first. The precipitation of snow upon them 

 must therefore have been cumulative, until the oceans 

 were reduced to about the point of maximum density. 



It is reasonably certain that glacial conditions were 

 first removed from equatorial regions, and that maxi- 

 mum glaciation of land areas in temperate latitudes may 

 have occurred subsequent to the inauguration of solar 



