THE TERRESTRIAL DISTRIBUTION OF RADIUM 15 



Radium per Gram of Igneous Rocks in Billionths (io -11 ) 



of a Gram 



The number of rocks included in the averages is given in the first of 



each pair of columns 



* Alkaline rocks. 



+ Composite analyses. 



Prof. Joly's results may also be expressed in the following 

 form, which brings out the connection between the mode 

 of occurrence of igneous rocks and their radium contents. 

 As before, the latter are stated in billionths (10 -12 ) of a gram per 

 gram of rock. 



My own composite analyses were made by applying the 

 solution method to the three following sets of well-known 

 rocks, and the results obtained are given here because they 

 appear to fill important gaps in the data hitherto published. 



1 Strutt, Proc. Roy. Soc, A., vol. lxxvii. p. 472, 1906. 



2 Eve and Mcintosh, Trans. Roy. Soc. Canada, series iii. p. 69, 1910. 



3 Farr and Florance, Phil. Mag. vol. xviii. p. 812, November, 1909. 



4 Schlundt and Moore, Bull. U.S.G.S. 395, 1909. 



s Buchner, Proc. Kon. Akad. v. Weten, Amsterdam, vol. xiii. p. 359, 1910; 

 vol. xiii. p. 818, 191 1 ; vol. xiii. p. 1063, 1912. 



6 Fletcher, Phil. Mag. vol. xx. p. 36, July 1910; vol. xxi. p. 102, January 191 1 ; 

 vol. xxi. p. 770, June 191 1. 



7 Holmes, The Age of the Earth, London, 191 3, pp. 130 and 182. 



5 Joly, Phil. Mag. vol. xxiv. p. 694, October 1912. 



