668 EDITORIAL 



disconformities, while to others of lesser duration in general Barrell 

 would apply the term "diastem." The recognition of diastems 

 and disconformities greatly lengthens the estimates of geologic 

 time based on sedimentation. This discussion is followed by a 

 review of all previous estimates of geologic time, distinguishing 

 those based on oceanic salts and on radioactivity. The latter is 

 fully and favorably presented. The paper closes with a section 

 on the convergence of evidence, in which the physical terrestrial 

 phenomena are compared with those of biologic evolution and 

 stellar evolution. The trend of the argument is toward the accept- 

 ance of a very great age for the earth, possibly fifteen hundred 

 million years. But, on the other hand, the amount of solar energy 

 due to gravitational infall is found to be but approximately i per 

 cent of that which would have been radiated during that immense 

 lapse of time, and Barrell is thus led to consider the probability 

 that there are other sources of energy in the sun than gravitational 

 condensation. He recognizes that the great concentrations of 

 energy must have previously been stored, and concludes: "The 

 scheme of the universe is more profound and the unknown is a 

 little nearer than it was recently thought to be. " 



The planetesimal hypothesis of the genesis of the planets has 

 taken a permanent place among the foundations of geologic theory 

 in America. Reviewing Chamberlin's Origin of the Earth Barrell 

 wrote: 



To gain a proper appreciation of the value of the investigations which 

 are condensed in this volume we must compare the present state of thought 

 upon the general subject with that of twenty years ago, before Chamberlin 

 had begun to pubhsh upon the hypotheses of earth-genesis. Measured by 

 that perspective, this volume is seen to represent an advance in thought on 

 this subject so great that the names of Chamberlin and Moulton must rank 

 high among those scientists who have dealt constructively with that vast, 

 vague, and remote problem, the origin of the earth. The subject of earth- 

 genesis is now fairly on the road to scientific investigation in place of philosophic 

 speculation.^ 



It was characteristic of Barrell that he should translate the 

 thought of the last sentence into action and should proceed to 

 investigate the subject of earth-genesis by applying tests to Cham- 

 berlin's hypothesis, or rather to the group of multiple hypotheses, 

 some of which were .adopted and some discarded by Chamberlin in 



^ Science, 191 6. 



