DISTRIBUTION OF RADIOACTIVITY IN DEPTH 143 



conditions for aqueo-igneous fusion and for the formation of granitic 

 rocks from rhyolitic and trachj'tic massives. 



Thus the formation of primitive granitic rocks may rationally be con- 

 ceived as due to a refusion immediately following the consistentior status 

 and extending as far from the surface as aqueous vapors could penetrate. 

 How far that would be it is, to be sure, as yet impossible to say — a mile 

 or two at least, it may be guessed, but probably not many miles. 



The thermal relations of the formation of primeval granite, as sketched 

 above, are complex. Aqueous vapor was condensed and united with the 

 rhyolitic material to a magma of a lower temperature than the rock had 

 possessed before aqueo-igneous fusion. Heat was liberated by the con- 

 densation of the vapor and the cooling of the magma, but heat was ab- 

 sorbed by the liquefaction of the rock. Now the absorption of heat in the 

 dry fusion of orthoclase is small, and I know of no indication that it 

 would be great in the aqueo-igneous fusion of granite, while the heat 

 liberated by the condensation of aqueous vapor is, of course, enormous. 

 Though no exact balance can be struck, it would seem as if the primeval 

 granite must have formed very slowly indeed, unless by some means sur- 

 plus energy could be potentialized. In the absence of such a disposition 

 of the excess, granite could form only as fast as radiation from the sur- 

 face reduced the temperature at internal levels to the point at which 

 silica crystallizes as quartz. On the other hand, if energy could be poten- 

 tialized within the mass, the tendency to stable thermal equilibrium would 

 be fulfilled with comparative rapidity, and such tendencies usually involve 

 adjustment at a maximum rate. 



The bounds of legitimate hypothesis are not transgressed by supposing 

 that the surplus energy of aqueo-igneous refusion was potentialized by 

 the formation of uranium, and that the energy of radioactive matter 

 thus represents a part of the original energy of the cooling globe. If so, 

 the solidification of the primeval granite was hastened by the genesis of 

 uranium, and the heat which now escapes from its disintegration products 

 would have been radiated into space long since if no such complex atoms 

 had been stable under the conditions of aqueo-igneous fusion. The earth 

 has cooled more gradually because of an endothermic reaction, but the 

 source of its heat is dynamic. 



Although there is reason to believe that the radium content of the 

 rocks is at a maximum in or just below the vadose waters, this does not 

 affect the computation of the total amount of radium from the difference 

 between the normal gradient and the gradient for a given age. This 

 follows from the assumption that all the heat generated by the disintegra- 

 tion of radium is emitted from the surface and in so far its distribution 



