26 ORGANIC DEPENDENCE AND DISEASE 



had the longer life, its type was locked up almost from the 

 start, and except for the lesson it teaches of stagnation and 

 decline, we might say, without impiety, that its conservation 

 has been a waste of time. And it is a type, too, that was 

 won, not by the arduous struggles of the ages, but arrived 

 at early and with ease. Therefore its lessened worth. 



DIVISIONS OF GEOLOGICAL HISTORY 



We cannot well proceed with this discussion without a 

 succinct statement here of the stages of geological history, 

 in which special emphasis is laid upon those earlier di- 

 visions with which we are especially concerned. The table 

 that follows is a condensed one of standard acceptance ; it 

 begins at the top of the latest life-bearing rocks and ends 

 with the oldest. As to the estimates of time represented 

 for the deposition of these sediments and for the existence 

 of the life of the earth, this must be said: Ten years 

 ago there was considerable variance of opinion be- 

 tween the physicists who were estimating the age of the 

 planet on the basis of the external disturbances to which it 

 was subjected in our planetary system, and the geologists 

 who sought to approach this problem from measurements 

 of the rate of deposition and erosion of water-laid sedi- 

 ments ; but a conservative conclusion had been provisionally 

 attained which was tacitly accepted by most geologists as 

 somewhere between sixty and one hundred million years 

 for the sum of all water-laid rocks and perhaps from forty 

 to sixty million years for those rocks which still carry the 

 obvious remains of life. Since the discovery of radium and 

 with a growing understanding of the significance of radium 

 decomposition and radio-activity these estimates have been 

 enormously outstripped, so vastly indeed that the very size 

 of the figures seems to put them under suspicion. The time 

 element in this is still a factor of much discussion and 



