CLARKE— THE AGE OF THE EARTH. 275 



This is a relative expression, but we can not be more concrete. 

 The Walcott discoveries have lifted the veil from a scene in the 

 panorama of life that was barely guessed before. In our previous 

 general understanding there was, in the still earlier faunas, a group 

 of creatures believed to be of simple structure and lowly place in the 

 category of lif e ; it was thought that with these simple things the 

 caravan of life had got under way for its journey through the ages; 

 and now we are compelled to believe that the journey was half over 

 when this caravan first came under our eye. 



It is not my part to make a review of statements and calculations 

 of earth age based on the rates of sedimentation from the Cambrian 

 time on to the present; but whatever these are, they may, from the 

 biological point of view, reasonably be doubled and then increased by 

 some improper fraction, if we are to reach a competent expression of 

 the duration of the life-day of extinct species — the zoehemera, as I 

 termed it many years ago, and of the sum of these which go to make 

 a fraction of earth history. 



It has not been the practice of students of evolutionary pale- 

 ontology to raise the question as to whether there were time enough 

 available for the production of the succession of results which pass 

 under their eye. Such an attitude would of itself be highly unphilo- 

 sophical, and only a natural inquisitiveness or curiosity quite unessen- 

 tial to the real philosophy of the succession and purpose of life has 

 led to the occasional investigation as to the possible time-rate of 

 evolutionary processes under historic and under natural conditions. 

 We are not the makers, but the users, of time. There have been 

 stages in the history of our science when we have been treated gin- 

 gerly by astronomers and physicists in the allotment of time, but now 

 that our colleagues in celestial mechanics are heaping upon us their 

 munificence in the prescription of this heavenly commodity, we are 

 content ; and the interpreters of radio-chemistry — we thank them for 

 giving us what we already had. There is time enough. So much, 

 indeed, that to absorb a needful share of it into the philosophy of the 

 evolution of life actually requires of us a revision of our conceptions. 



I should, I think, take passing notice of the fact that the problem 

 as to how species have originated, one from another, with or without 



