470 Mr. J. H. J. Poole on the Radium Content 



Table II. 



Number Mean 



Rock. of Radium 



Specimens. Content 



Granite 7 2*3 



Limestone 16 To 



Talc Schist 16 2-0 



Quartz Schist 12 2'4 



Mica Schist 2 2"1 



Hornblende Schist 2 31 



Schist Lustre 2 3'4 



Felspathic Schist 3 27 



Schist (Unclassified) 16 2'5 



Aplite 2 2-5 



Quartz Porphyry 1 2*5 



Anhydrite 2 M 



Quartz Sandstone 1 4'3 



Mean Radium Content for all schists (53 Specimens) 

 = 2-4 Xl0~ 12 g' 1 ^- per grin. 



Mean Radium Content for all rocks (82 Specimens) 

 = 2'2xl0~ 12 grin, per grm. 



With regard to the mean results given in Table II., it may 

 be remarked that the radium content of the Gastern Granite 

 appears to be rather low. Dr. Joly obtained a radium con- 

 tent of 2'7 x 10~ 12 grm. per grm. of rock from a composite 

 rock powder in which 63 granites from various localities 

 were represented. The discrepancy between this figure and 

 that of 2'3 x 10~ 12 is, however, not so large as it appears, for 

 if we neglect one abnormally low value of 1*3 X 10 ~ 12 , which 

 was obtained from a specimen just near the junction of the 

 limestone and the granite, we obtain a mean for six speci- 

 mens only of 2*5 x 10" i2 ; a result which is not much below 

 the mean radium content for granites previously quoted. It 

 may be of interest to note in passing that there seems to be 

 a certain indication in Table 1. that the centre of the Gastern 

 Granite Massif is more radio-active than the edges ; but 

 there are not really enough specimens to be absolute^ sure 

 of this fact. 



On the other hand, the mean radium content, both for 

 the calcareous and schistose rocks, seems to be, on the 

 whole, higher than the average value for calcareous rocks. 



