302 POPULAR LECTURES AND ADDRESSES. 



of underground temperature, in places where the 

 date is known of a recent disturbance, would 

 be of great importance, and would give us the 

 means of inferring something regarding the geo- 

 logical history of places where an extraordinary 

 rate of increase is observed. It is not, however, 

 my purpose, at present, to enter into any specu- 

 lation regarding geological dates in cases such 

 as these, but rather to put before you con- 

 siderations with respect to underground tempera- 

 tures in general, which in the first place seem 

 to indicate internal fluidity, but which, when 

 further studied, do not really lead us to any such 

 conclusion, but rather lead us to suspend our 

 judgment, and to look in other directions for 

 evidences of the internal condition of the earth as 

 to whether it is fluid or solid. 



I'Yom the observed increase of temperature 

 downwards below ground in all localities, we must 

 conclude that the earth had, at some time more or 

 less remote, its whole surface at some very hii;h 

 temperature. It may have been reel-hot and solid 

 all round ; but it is far more probable that the 



