ON GEOLOGICAL TIME. 55 



of temperature downwards, they say they have not 

 evidence enough to show that there is increase 

 of temperature downwards in all parts of the earth, 

 or enough of evidence to allow us to say that the 

 theory that accounts for underground heat, by 

 local chemical action, may not be true. This 

 being the state of the case as regards underground 

 heat, where must we apply to get evidence ? 

 Observation ; observation only. We must go 

 and look. We must bore the earth here in the 

 neighbourhood. We must examine underground 

 temperature in other places. We must send out 

 and bore under the African deserts, where water 

 has not reached for hundreds of years. The whole 

 earth must be made subject to a geothermic survey. 

 Having been deeply impressed with these views 

 for many years, I have long endeavoured, in vain, 

 to call the attention of geologists to them. I now 

 feel very greatly indebted to the Geological Society 

 of Glasgow, for giving me the opportunity of 

 speaking of them this evening. I may be allowed 

 to add that on the occasion of the recent meeting 

 of the British Association, at Dundee, the import- 



