256 CHAMBERLIN— THE AGE OF THE EARTH. 



vidual contribution. It is thus possible to sum up as many of these 

 separate contributions as can be measured satisfactorily and rest the 

 case there, leaving what remains of the earth's age to be found out 

 later or to be guessed at or to be ignored. But when the inquiry 

 turns to the solutions it must face the fact that the contributions of 

 each stage have been mingled with those of all other stages and the 

 record to be measured is thus an indivisible unit. If the ocean, con- 

 sidered as such record, can be used to measure age at all, it is the 

 total age of the ocean. This total age of the ocean can not be ex- 

 pected to tally with the age found from an unknown fraction of 

 sediments. 



The Basis of Estimating the Age of the Ocean. — The interpreta- 

 tion of the time occupied in the concentration of solutions in the ocean 

 hangs on the assumptions made relative to its origin and to the entire 

 history of the earth's waters on land and sea alike. This includes 

 the volume of the waters at the start and all along; it includes the 

 metamorphic solutions from within the earth as well as those that 

 arise from surface action. Account must also be taken of such 

 reversals of action as take material out of solution and return it to 

 the solid state. All these must be considered, for they are all neces- 

 sarily involved in the question of the age of the ocean. Some basal 

 assumptions are unavoidable, and if we must deal with them, it is 

 best to be frank and explicit about them. The necessary assumptions 

 as to the early stages of the ocean are more or less speculative, but 

 if we are to discuss the question of age at all, there is no occasion to 

 be squeamish about that. It does not make the assumptions any less 

 " speculative " to gloss over or shy at the fact that they are speculative 

 or at least have speculative factors. Assumptions are least dangerous 

 when explicitly recognized. They are even likely to be least specu- 

 lative when the grounds on which they rest are carefully sifted, logi- 

 cally weighed, and made to throw such light as they may on the ques- 



critical points was impracticable. The printed text gives somewhat more 

 liberty and I have taken advantage of it to a limited extent and have recast 

 this part of the text to accommodate it to this. I am greatly indebted to Dr. 

 T. Wayland Vaughan, U. S. Geologist in Charge of Investigations on Sedi- 

 ments, for aid in securing documents and personal statements from the de- 

 partments of our general government and from its officials engaged in investi- 

 gations bearing on the question in hand. 



