AGE OF THE EARTH JOLY. 293 



transformation products in minerals, in place of being a measure of 

 geologic time, serves to shed light upon the rate of transformation 

 of the primary radioactive bodies in the past. Apart from its interest 

 in other respects, the importance of such a conclusion to geologic 

 science would be great. If we supposed the curve, found by plotting 

 the time results derived from lead ratios against the sedimentary 

 thicknesses, represented an approximation to the facts, the rate of 

 change of uranium 150,000,000 years ago may have been many times 

 what it now is. The radiothermal effects of the whole series must 

 have been proportionately increased, and the convergence of the 

 radioactivity must have had an influence upon the secular cooling of 

 the earth. 



July 18, 1911. 



