680 T. C. CHAMBERLIN 



concluded that a distribution of radioactive substance equal to 

 that of the surface rocks for a depth of only 45 miles would give 

 the rise of heat actually observed in wells, mines and other deep 

 excavations. Later data and closer scrutiny seem to confirm the 

 general soundness of Strutt's inference, and to make the limita- 

 tions even more narrow. Joly, approaching the problem from the 

 geological as well as the physical point of view, and with the 

 advantage of later data, reached the conclusion that radioactivity 

 of the amount observed at the surface, if continued to a depth 

 ranging from 27 to 37 kilometers (17.2 to 23.5 miles), would give 

 rise to heat equal to that implied by the loss at the surface. 1 Accord- 

 ing to Joly, however, a complete concentration of radioactivity 

 in a shell of this depth does not meet the apparent requirements 

 of igneous phenomena if this be assigned to radioactivity. A 

 deeper distribution of a part of the radioactive matter and a less 

 concentration in the outer part of the crust is felt by Joly to be 

 required and he was led to this final statement: "If we said that 

 the richer part of the crust must be between 9 and 15 kilometers 

 deep, we cannot be far from the truth. This appears to be the 

 best we can do on our present knowledge." 2 It is to be noted that 

 these deductions are reached on the supposition that all the internal 

 heat given out arises from radioactivity; no margin is left for any 

 original heat or for secular heat from any other source. On the 

 other hand, the computations seem to take no account of loss of 

 heat by means of igneous extrusions. 



These remarkable deductions raise two questions of radical 

 import : 



(1) If supplies of heat are generated currently by radioactivity 

 in such abundance that it is necessary to put these severe limits 

 on the distribution of radioactive substances, must we abandon 

 entirely all further consideration of supposed supplies handed down 

 from a white-hot earth or from any other form of the primitive 

 earth ? 



(2) Is there among the internal processes previously postu- 

 lated any that provides a way in which such a concentration at 



1 Radioactivity and Geology (1909), 175. 



2 Ibid., 183. 



