﻿Radium Content of Secondary Rocks. 



291 



Summary. 



The outstanding features of these results are (with the 

 exception of the calcareous rocks) the persistence of the 

 radium in consistent and nearly identical quantity from one 

 rock type to another, and, with the same exception, their 

 almost unvarying sameness in rocks of one type. Practically 

 speaking, all the secondary rocks with the exception of those 

 of calcareous nature contain approximately the same quantity 

 of radium per gram, as w T iil be seen from the figures below, 

 but the differences though small may, in view of the large 

 number of individual experiments performed, be regarded as 

 positive. An explanation of the lower quantities of radium 

 contained in the less important calcareous rocks has been 

 given by Professor Joly *, and the results were therefore in 

 this instance anticipated. 



Table of Mean Results. 



Rock Type. 



Number of 



expts. on 



which average 



is based. 



Radium 

 in grams 

 per gram. 



Coarse detrital Sediments 



Coarse detrital Sediments (Metamorphosed) ... 

 Fine detrital Sediments (Argillaceous) 



24 

 9 



16 



9 

 24 



1-5x10-12. 



1-5 



13 



IT 



0-8 



Fine detrital Sediments (Schistose) .' 



Calcareous Sediments 





It would be misleading to include the large number of 

 calcareous rocks investigated in a general mean, because they 

 actually comprise but a small percentage (estimated at almost 

 5 per cent.) of the general sedimentary rocks of the earth's 

 crust. The mean of the remaining specimens, 58 in number, 

 is say 1*4 x 10 -12 gram per gram. 



I have to thank Professor Joly for his unfailing interest 

 and constant advice throughout the course of these 

 experiments. 



Geological Laboratory, 

 Trinity College, Dublin, 

 December, 1911. 



Radioactivity and Geology, 1 p. 51, 



