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. 
