﻿Archcean 
  Rocks 
  from 
  the 
  Mysore 
  State. 
  209 
  

  

  (Numbers 
  in 
  brackets 
  refer 
  to 
  the 
  classification 
  given 
  above.) 
  

  

  Kadiuni, 
  gm. 
  per 
  

  

  Group. 
  

  

  fHornblendic 
  series 
  (12) 
  

  

  JDiiarwarJ 
  n 
  ., 
  altered 
  types 
  

  

  j 
  Ohloritic 
  series 
  (11) 
  

  

  ^ 
  Basic 
  iutrusives 
  (11) 
  and 
  (12) 
  .. 
  

  

  Champion 
  gneiss 
  (10) 
  

  

  „ 
  ,, 
  auriferous 
  quartz 
  

  

  Peninsular 
  gneiss 
  (9) 
  

  

  „ 
  ,, 
  pegmatites. 
  

  

  Charnockites 
  (7) 
  

  

  „ 
  hypersthenite 
  (6) 
  

  

  „ 
  quartz-magnetite 
  ore 
  

  

  10 
  12 
  gm. 
  of 
  rock. 
  

  

  Limits. 
  

   0-14 
  to 
  0-25 
  

   0-34 
  „ 
  0-96 
  

   0-20 
  „ 
  0-54 
  

   0-05 
  „ 
  0-16 
  

  

  Closepet 
  granite 
  (5) 
  

  

  ,, 
  ., 
  porphyries 
  (4). 
  

  

  Dolerite 
  dykes 
  (Post-Archagan) 
  (3) 
  

  

  0-85 
  to 
  1-45 
  

   1-28 
  

  

  0-40 
  to 
  1-50 
  

   1-44 
  to 
  6-90 
  

  

  0-04 
  to 
  0-12 
  

   0-06 
  

   008 
  

  

  0-27 
  to 
  2-14 
  

   1-37 
  „ 
  2-42 
  

  

  0-45 
  

  

  The 
  hornblendic 
  rocks 
  of 
  the 
  Dharwar 
  System 
  (Nos. 
  1-18) 
  

   are 
  low 
  in 
  radium 
  and 
  exhibit 
  no 
  great 
  variation 
  from 
  the 
  

   mean, 
  though 
  many 
  penological 
  types 
  are 
  included, 
  such 
  as 
  

   hornblende 
  schists, 
  hornblende 
  diabases, 
  amphibolite, 
  and 
  

   hornblende 
  granulite. 
  When, 
  however, 
  these 
  rocks 
  are 
  

   altered 
  in 
  contact 
  with 
  intrusions 
  of 
  the 
  Champion 
  gneiss 
  

   and 
  of 
  the 
  related 
  quartz 
  veins 
  of 
  the 
  Kolar 
  Field 
  (Nos. 
  26- 
  

   30), 
  all 
  of 
  which 
  contain 
  much 
  more 
  radium 
  than 
  the 
  

   normal 
  schists, 
  the 
  radioactivity 
  of 
  the 
  altered 
  types 
  is 
  con- 
  

   siderably 
  increased 
  (Nos. 
  12, 
  15, 
  and 
  16) 
  to 
  a 
  point 
  inter- 
  

   mediate 
  between 
  the 
  radioactivities 
  of 
  the 
  two 
  reacting 
  

   masses. 
  

  

  The 
  rocks 
  of 
  the 
  Ghloritic 
  series 
  (Nos. 
  19-21) 
  do 
  not 
  appear 
  

   to 
  differ 
  much 
  in 
  radium 
  from 
  those 
  of 
  the 
  hornblendic 
  series. 
  

   The 
  higher 
  value 
  in 
  No. 
  21 
  may 
  possibly 
  be 
  the 
  result 
  of 
  

   alteration 
  due 
  to 
  a 
  neighbouring 
  granitic 
  intrusion. 
  

  

  The 
  basic 
  intrusives 
  of 
  Dharwar 
  age 
  — 
  that 
  is 
  to 
  say, 
  intru- 
  

   sive* 
  into 
  the 
  general 
  body 
  of 
  the 
  Dharwar 
  schists 
  prior 
  to 
  

   the 
  period 
  of 
  the 
  Peninsular 
  gneiss 
  — 
  contain 
  much 
  less 
  

   radium 
  than 
  even 
  the 
  schists 
  themselves. 
  This 
  is 
  particularly 
  

   noticeable 
  in 
  the 
  Bellara 
  trap 
  (No. 
  23) 
  and 
  the 
  Grey 
  trap 
  of 
  

   Chitaldrug 
  (No. 
  21), 
  and 
  these 
  rocks 
  afford 
  an 
  interesting 
  

   example 
  of 
  the 
  possible 
  use 
  of 
  such 
  determinations 
  in 
  the 
  

   correlation 
  of 
  these 
  very 
  old 
  and 
  much 
  altered 
  Archsean 
  

   types. 
  Some 
  years 
  ago 
  the 
  Grey 
  trap 
  was 
  considered 
  to 
  be 
  

   a 
  modification 
  of 
  the 
  less 
  altered 
  Bellara 
  trap, 
  but 
  subsequent 
  

  

  