of the Radio-active Elements. 87 



tegrate per second, and, for our present purposes, we can 

 neglect the difference in atomic weight and simply assume that 

 in any time the weights of radium and uranium which undergo 

 transformation are the same. In one gram of uranium the 

 weight of uranium which would be transformed in one year 

 would therefore be 2-7-10" 4 X3-8-10- 7 = lO" 10 gram, and the 

 fraction of uranium transformed per year would be 10 -10 . 



In the table which follows (Table VI) the ages of the min- 

 erals included under Table I have been roughly calculated in 

 accordance with the method outlined above. The ages of the 

 minerals in years are obtained by multiplying the average 

 value of the ratio 10 10 . The general plan of calculating the 

 ages of the minerals in this manner was first suggested to the 

 writer by Prof. Rutherford. 



Table VI. 

 T ,., Age of minerals 



Locallt y- in million years. 



Glastonbury (Portland), Conn. 410 



Branchville, Conn. . .... 535 



Spruce Pine, N. C - 510 



Marietta, S. C 460 



Llano and Burnet Co., Texas .. 1800 



Douglas Co., Colorado 1 900 



Moss District, Norway 1300 



Annerod, Norway 1 700 



Sabaragamuwa Prov., Ceylon 2200 



Galle District, Ceylon 860 



The actual values obtained for these ages are, of course, 

 dependent on the value taken for the rate of disintegration of 

 radium. When the latter has been determined with certainty, 

 the ages as calculated in this manner will receive a greater 

 significance, and may perhaps be of considerable value for 

 determining the actual ages of certain geological formations. 



Disintegration Products of Thorium. 



The available data on the composition of the radio-active 

 minerals serve to throw some light on the nature of the dis- 

 integration products of thorium as well as uranium. The rela- 

 tive proportions of uranium and thorium may show large 

 variations in minerals from the same locality without exercis- 

 ing a noticeable effect on the value of the lead-uranium ratio 

 for that locality. It can therefore be concluded with certainty 

 that lead is not a disintegration product of thorium. This 

 fact is particularly emphasized by the composition of the 

 thorite found with the thorianite in the Sabaragamuwa prov- 

 ince of Ceylon and in all probability of contemporaneous 



