GEOLOGICAL CLIMATE. 297 



which geological investigation teems, of warmer 

 climate all over the earth from equator to poles 

 in the more ancient geological periods. Under- 

 ground heat, though certainly greater in the 

 earlier geological times, cannot, as I have shown 

 elsewhere, 1 have ever sensibly influenced the 

 climate. Ten, twenty, thirty times the present 

 rate of augmentation of temperature downwards 

 could not raise the surface temperature of the earth 

 and air in contact with it by more than a small 

 fraction of a degree Fahrenheit. The earth might 

 be a globe of white hot iron covered with a crust 

 of rock 2000 feet, or there might be an ice-cold 

 temperature everywhere within 50 feet of the 

 surface, yet the climate could not on that account 

 be sensibly different from what it is, or the soil be 

 sensibly more or less genial than it is for the roots 

 of trees or smaller plants. Yet greater under- 

 ground heat is the hypothesis which has been 

 most complacently dealt with by geologists to 

 account for the warmer climates of ancient times. 



1 Secular Cooling of the Earth, Trans. R.S.E., 1862, and Thorn 

 son and Tail's Natural Philosophy, Vol. I. , App. D. 



