GEOLOGICAL SEASONS. 



A CCORDING to the accepted theory of terrestrial refrig- 

 *-*- eration, the inherent temperature of the earth is 

 continually diminishing. So far as its climates are influ- 

 enced by inherent temperature, they must continually grow 

 colder. Before the earth began to be incrusted a circula- 

 tion of its constituent parts must have been active. Loss 

 of heat in the peripheral portions would result in a sink- 

 ing of those condensed portions toward the center. More 

 highly-heated portions would rise to supply their place. 

 Thus, as in the sea, and in the atmosphere, a circulation 

 would result from the unequal temperatures of different 

 portions. 



But after the commencement of incrustation those por- 

 tions fixed in the crust would no longer enter into the cir- 

 culation. The superficial portions would remain continu- 

 ally exposed to the cooling action of external space. The 

 effect of this would be to depress the superficial tempera- 

 ture below what it would be if all the parts were free to 

 circulate. The crust would become disproportionately 

 cooled, and would continually thicken. The cooling of the 

 interior would be proportionally slackened. The time 

 would arrive when the cooling of the interior would be so 

 much obstructed as to be almost imperceptible. That 

 period seems to be the present. If we may trust the re- 

 sults of mathematical calculation, based on the known 



175 



