Radioactivity of Rocks of the Kolar Gold Fields, 49 



The Results. 



Mr. H. M. A. Cooke of Kolar very kindly supplied us 

 with large specimens of " country rock " selected at varying 

 depths from each of the chief mines. These were fir si, 

 roughly crushed iu order to obtain fair samples. 



The following table shows the amount of radium per gram 

 of rock in units of 10 ~ 14 gram. 



The depths from which the samples were taken are only 

 approximate, and are measured along the incline of the shaft. 

 The actual vertical depths are usually considerably less, for 

 instance, 4000 feet on the incline in the Mysore mine is only 

 2664 feet below the surface. As, however, the shafts follow 

 the direction of the strata, a comparison made in this way is 

 probably preferable to one made at equal vertical depths. 



The names of the mines are given as they occur geogra- 

 phically, Balaghat being the most northerly. 



Table I. 



Name of Mine. 



Depth in feet. 



1000. 



2000. 



3000. 4000. 



Balaghat 



21 

 17 

 18 



34 



14 



17 

 24 



21 



21 



Nundidroog 



14 



91 







]8 14 

 23 96 



Mysore 









It will at once be seen from the above that there is no 

 obvious relation between the radium content and the position 

 of the rock; and in fact, with two exceptions, the numbers are 

 almost the same within the limit of experimental error. It 

 thus appears that the distribution of radium is uniform. 



With regard to the high value for the deepest sample from, 

 the Mysore mine, a second experiment showed the figure to 

 be correct; but it was found on subsequent examination that 

 the rock was of quite a different character to the others, being 

 probably a later formation. 



A few other samples of rock, the geological history of 

 which was known to some extent, were kindly presented to 

 us by Dr. Smeeth of the Mysore Geological Department, and 

 the radium content was determined. As these rocks were of 



Phil. Mag. S. 6. Vol. 28. No. 163. July 1914. E 



