﻿Archcean 
  Rocks 
  from 
  the 
  Mysore 
  State. 
  207 
  

  

  An 
  account 
  of 
  the 
  method 
  used 
  and 
  results 
  obtained 
  was 
  

   published 
  in 
  the 
  Philosophical 
  Magazine 
  (6) 
  xxviii. 
  p. 
  44, 
  

   1914, 
  and 
  the 
  results 
  are 
  repeated 
  in 
  Table 
  I., 
  Nos. 
  1 
  to 
  15. 
  

   It 
  will 
  be 
  seen 
  that 
  the 
  radium 
  content 
  is 
  very 
  low, 
  remark- 
  

   ably 
  constant, 
  and 
  that 
  there 
  is 
  no 
  variation 
  in 
  depth 
  down 
  

   to 
  a 
  vertical 
  depth 
  of 
  some 
  3500 
  feet 
  from 
  the 
  surface. 
  

  

  Two 
  of 
  the 
  samples 
  — 
  Nos. 
  12 
  and 
  15 
  — 
  gave 
  results 
  con- 
  

   siderably 
  higher 
  than 
  the 
  others, 
  but 
  microscopic 
  examination 
  

   showed 
  that 
  these 
  samples 
  did 
  not 
  represent 
  normal 
  types 
  of 
  

   the 
  hornblendic 
  schists 
  or 
  " 
  country 
  " 
  of 
  the 
  mines, 
  but 
  had 
  

   undergone 
  considerable 
  mineral 
  alteration, 
  such 
  as 
  is 
  common 
  

   in 
  the 
  immediate 
  vicinity 
  of 
  the 
  quartz 
  veins 
  or 
  other 
  acid 
  

   intrusives, 
  and 
  there 
  is 
  no 
  doubt 
  that 
  the 
  higher 
  values 
  are 
  

   due 
  to 
  the 
  intrusion 
  of 
  acid 
  material 
  of 
  higher 
  radium 
  

   content. 
  

  

  Further 
  Investigation. 
  

  

  It 
  was 
  then 
  decided 
  to 
  obtain 
  a 
  number 
  of 
  representative 
  

   samples 
  from 
  the 
  various 
  components 
  of 
  the 
  Archsean 
  com- 
  

   plex 
  of 
  Mysore, 
  in 
  order 
  to 
  ascertain 
  how 
  far 
  the 
  various 
  

   formations 
  or 
  groups 
  might 
  be 
  distinguishable 
  from 
  one 
  

   another 
  by 
  their 
  radioactivity, 
  and 
  what 
  variations 
  existed 
  

   amongst 
  the 
  members 
  of 
  each 
  group 
  as 
  a 
  result 
  of 
  magmatic 
  

   segregation. 
  The 
  experimental 
  procedure 
  was 
  the 
  same 
  as 
  

   before, 
  viz., 
  10 
  gms. 
  of 
  the 
  finely 
  powdered 
  rock 
  were 
  fused 
  

   with 
  potassium 
  hydroxide, 
  under 
  reduced 
  pressure, 
  and 
  the 
  

   resulting 
  gases 
  led 
  to 
  an 
  electroscope 
  after 
  removal 
  of 
  the 
  

   hydrogen 
  and 
  drying. 
  Towards 
  the 
  middle 
  of 
  the 
  experi- 
  

   ments 
  the 
  leaf 
  system 
  in 
  the 
  electroscope 
  broke 
  down, 
  and 
  

   was 
  replaced 
  by 
  a 
  smaller 
  and 
  more 
  sensitive 
  one, 
  which 
  was 
  

   subsequently 
  carefully 
  standardized. 
  With 
  this 
  a 
  leak 
  of 
  

   1 
  scale 
  division 
  an 
  hour 
  corresponded 
  to 
  1*67 
  x 
  10 
  -13 
  gm. 
  of 
  

   radium. 
  Control 
  experiments 
  showed 
  no 
  discontinuity 
  be- 
  

   tween 
  the 
  two 
  series 
  of 
  values 
  obtained. 
  All 
  experimental 
  

   details 
  have 
  already 
  been 
  given 
  (loc. 
  cit.), 
  and 
  will 
  not 
  be 
  

   repeated. 
  Altogether, 
  fifty 
  samples 
  have 
  been 
  selected 
  from 
  

   specimens 
  in 
  the 
  Department 
  of 
  Mines 
  and 
  Geology 
  of 
  

   Mysore 
  and 
  the 
  radium 
  determined, 
  but 
  each 
  group 
  is 
  itself 
  

   so 
  complex 
  and 
  variable 
  that 
  a 
  much 
  larger 
  number 
  would 
  be 
  

   required 
  before 
  fair 
  averages 
  or 
  estimates 
  could 
  be 
  obtained. 
  

   In 
  spite 
  of 
  this, 
  certain 
  interesting 
  variations 
  appear 
  to 
  be 
  

   indicated, 
  and 
  the 
  results 
  obtained 
  have 
  been 
  grouped, 
  in 
  

   Table 
  L, 
  under 
  the 
  various 
  formations 
  taken 
  in 
  order 
  of 
  age 
  

   from 
  the 
  oldest 
  to 
  the 
  youngest. 
  

  

  Q2 
  

  

  