BEARINGS OF RADIOACTIVITY ON GEOLOGY 675 



affects the progress of radioactive decomposition, but no specific 

 effects of a critical value have been certainly disclosed by experi- 

 mentation. These conditions that so much qualify most geologic 

 processes must apparently be regarded as negligible for the present 

 so far as radioactivity in the earth's crust is concerned. It is 

 thought by the leaders in radioactive science permissible to treat 

 radioactive substances as undergoing disintegration persistently 

 and uniformly under all known terrestrial conditions. In the 

 thermal problem of the earth radioactive particles may be dealt 

 with tentatively as centers of heat-generation whose efficiency and 

 endurance are conditioned simply by their atomic constitutions 

 and their mass values. In so far as these remarkable deductions 

 from experimentation may be thought to fall short of full warrant, 

 weakness in equal degree must of course be held to enter into the 

 geological inferences based on them; and in view of the radical 

 nature of the conclusions to which they lead, we cannot perhaps 

 too constantly bear in mind that the postulate of immunity to 

 conditions is the main basis of the geologic contributions credited 

 to radioactivity. But the remarkable verifications of skill and 

 accuracy that have followed the multiplication of tests furnish 

 an ample warrant for a serious discussion of present deductions. 

 There is strong presumption that future tests will further sub- 

 stantiate present conclusions so far as their main bearings on imme- 

 diate terrestrial problems are concerned, whatever interrogations 

 one may be disposed to indulge in regarding ulterior problems. 



The clue to this extraordinary tenacity of radioactive disso- 

 lution in spite of conditions that profoundly influence most ter- 

 restrial processes, probably lies in the fact that the action springs 

 from the internal motions of the atomic constituents and that 

 these are of such intense nature and are actuated by such pro- 

 digious energies that the influences of ordinary chemical and 

 physical conditions are relatively insignificant. 



At the same time, the radioactive substances show a decided 

 aptitude to enter into chemical combination under common con- 

 ditions. None of the parent radioactive metals is known to occur 

 in the earth in a native state. In the form of compounds they 

 have become widely distributed over the face of the globe in the 



