APPENDIX 321 



as excluding the hope of our finding the beginnings 

 of Hfe in any geological formations at present 

 known. 



Professor Poulton refers to the argument used 

 by Lord Salisbury, in his address at the Oxford 

 meeting, on the insufficiency of time for the require- 

 ments of the Darwinian evolution. He then dis- 

 cusses the estimates based by Lord Kelvin and 

 Professor Tait on physical considerations, and 

 dismisses them as altogether inadequate, though he 

 admits that Professor George Darwin agrees with 

 Lord Kelvin in regarding 500 millions of years as 

 the maximum duration of the life of the sun. 



He next takes up the estimates of geologists, 

 and rather blames as too modest those who ask 

 for the longest time, say 400 millions of years, for 

 the duration of the habitable earth. He evidently 

 scarcely deems worthy of notice the more moderate 

 demands of many eminent students of the earth, who 

 have based far lower estimates on more or less 

 reliable data of denudation and deposition, and on 

 the thickness of deposits in connection with their 

 probable geographical extent. 



He then proceeds to consider the biological evi- 

 dence, and dwells on the number of distinct types 



21 



