258 CHAMBERLIN— THE AGE OF THE EARTH. 



nition here, the one based on the view that the earth started as a 

 molten globe, the other that it grew up slowly by the accession of 

 solid particles. For the purposes of the present question it is not 

 radically material how the molten globe arose, on the one hand, nor 

 by what celestial mechanism the accretion took place, on the other, 

 beyond the fact that the material of the ocean was supposed to be 

 assembled as a vapor about a hot earth, in the one case, ready to begin 

 work in full volume when cooling took place, while in the other case 

 the waters came into action very gradually. Out of these basal dif- 

 ferences, however, there arise some important contrasts in the modes 

 of later action that are almost equally radical in their bearings on the 

 evolution of the ocean, so that both the original and derivative differ- 

 ences need to be sharply in mind in considering the question of the 

 earth's age. 



I. On the one hand, it is assumed that the ocean was essentially 

 uniform in volume throughout all the ages, and that the disintegration 

 of the surface rocks, the inflow of solutions, and the content they 

 carried were also essentially uniform. If these assumptions are cor- 

 rect, or if they hold true of a single leading element, as sodium, the 

 present rate and content of inflow may be used as a divisor to ascer- 

 tain the total time of inflow. This, however, is subject to the condi- 

 tion that there is no important reversal of action, or at least none that 

 can not be adequately measured and discounted. 



The alternative view assumes that the ocean grew to its present 



together unknown, had not beeri adequately recognized as indispensable cri- 

 teria in the interpretation of our planery system. In other words, the earth 

 and its family have dynamic peculiarities that make the question of their 

 origin a special one. These hereditary peculiarities point the way to their in- 

 terpretation. The planetesimal hypothesis is simply the result of an attempt 

 to follow these hereditary traits back to their parentage. It is as little as pos- 

 sible speculative, for it starts with mechanical properties which are rigorously 

 determinate and which must be met by any hypothesis of genesis worthy of 

 serious consideration. It follows these back to their probable origin in other 

 known properties and natural actions so related to them as to be their probable 

 sources. The method followed was only a phase of the standard practice of 

 geologists in following the vestiges of a recorded event back to their most 

 probable sources. If peculiar at all, it is merely in that the vestiges are dy- 

 namic. It ill becomes us to be squeamish about historical deductions from 

 historical vestiges for there are plenty of people who regard geology a specu- 

 lation from beginning to end and there is no present help for it. 



