﻿THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



FEBRUAR Y 1912. 



XVII. The Radioactivity of the Rocks of the St. Gothard 

 Tunnel By J. Joly, FM.S* 



IN 1908, in the course of a Presidential Address to 

 Section C of the British Association, I gave a summary 

 of: the results of my experiments on the radium content of 

 certain rocks from the St. Gothard tunnel. These results 

 showed considerably greater amounts of radium in the granite 

 at the northern end than elsewhere throughout the length 

 of the tunnel. 



The accompanying section (after Stapff ) shows the general 

 geological structure of the range through which the tunnel 

 passes. The granite extends for 2 kilometres from the north 

 entrance. It is the same granite which enters into the 

 structure of the Finsteraarhorn Massif. It is a coarsely 

 crystalline, rather gneissic, granite. At a point about 

 1000 metres from the entrance and for about f)00 metres 

 further there is considerable differentiation ; veins of various 

 differentiation products traversing the rock, chiefly of white 

 felspar, quartz, and a dense eurite. This region is indicated 

 by Staptf upon the section. After the granite the rocks 

 encountered (for a further distance of 2 kilometres) are 

 sedimentary, and exist in the form of two parallel sync-linos. 

 These rocks are believed to be of Trias-Jura age. and are 

 recognized without in the Usern district. They include 

 various altered sediments, some of which (as the Cipolin) 



* Communicated by the Author. 



Phil. Mag. S. 6. Vol 23. No. 134. Feb. 1912. P 



