﻿Thorium 
  in 
  the 
  Eartlis 
  Surface 
  Materials, 
  145 
  

  

  rocks 
  and 
  the 
  distribution 
  o£ 
  temperature 
  in 
  the 
  rocks 
  as 
  

   observed 
  during 
  the 
  progress 
  of 
  the 
  tunnel 
  ; 
  suggesting 
  that 
  

   the 
  observed 
  gradients 
  may, 
  in 
  fact, 
  be 
  referable 
  to 
  radio- 
  

   activity, 
  wholly 
  or 
  in 
  part. 
  It 
  will 
  be 
  seen 
  that 
  the 
  radio- 
  

   active 
  energy 
  due 
  to 
  thorium 
  must 
  also 
  be 
  predominant 
  in 
  

   that 
  region 
  of 
  the 
  tunnel 
  in 
  which 
  the 
  gradients 
  were 
  found 
  

   to 
  be 
  steepest 
  ; 
  that 
  is 
  in 
  the 
  Finsteraar 
  granite. 
  To 
  some 
  

   source 
  of 
  heat 
  in 
  this 
  granite, 
  Stapff 
  attributed 
  the 
  remarkable 
  

   gradients 
  obtaining 
  in 
  the 
  first 
  2000 
  metres 
  of 
  the 
  tunnel. 
  

   AVe 
  see 
  now 
  that 
  this 
  granite 
  is 
  not 
  only 
  richest 
  in 
  radium, 
  

   but 
  in 
  thorium 
  ; 
  for 
  however 
  variable 
  the 
  results 
  from 
  one 
  

   specimen 
  to 
  another 
  may 
  be, 
  the 
  added 
  testimony 
  of 
  the 
  22 
  

   radioactive 
  determinations 
  in 
  these 
  rocks, 
  and 
  of 
  the 
  80 
  

   measurements 
  elsewhere 
  throughout 
  the 
  tunnel, 
  can 
  hardly 
  

   be 
  deceptive. 
  As 
  observed 
  in 
  my 
  former 
  paper 
  on 
  the 
  dis- 
  

   tribution 
  of 
  thorium, 
  the 
  thermal 
  value 
  of 
  this 
  element 
  is 
  not 
  

   determinable 
  without 
  a 
  knowledge 
  of 
  its 
  rate 
  of 
  transformntion 
  

   or 
  an 
  experimental 
  determination 
  of 
  its 
  thermal 
  out-put 
  when 
  

   in 
  equilibrium 
  with 
  its 
  transformation 
  products 
  *. 
  

  

  The 
  quantities 
  of 
  thorium 
  observed 
  in 
  the 
  above 
  experi- 
  

   ments 
  appear 
  in 
  the 
  mean 
  to 
  come 
  out 
  as 
  roughly 
  proportional 
  

   to 
  the 
  quantities 
  of 
  uranium. 
  In 
  individual 
  experiments, 
  

   however, 
  a 
  comparison 
  of 
  the 
  radium 
  and 
  thorium 
  content 
  

   shows 
  that 
  very 
  often 
  such 
  a 
  relation 
  is 
  widely 
  departed 
  from. 
  

   The 
  net 
  result 
  is 
  to 
  ascribe 
  to 
  these 
  rocks 
  quantities 
  of 
  uranium- 
  

   and 
  thorium 
  which 
  are 
  not 
  very 
  different. 
  

  

  As 
  in 
  the 
  case 
  of 
  the 
  collective 
  radium 
  measurements 
  now 
  

   in 
  our 
  possession, 
  so 
  in 
  the 
  case 
  of 
  thorium 
  according 
  to 
  the 
  

   foregoing 
  observations, 
  sedimentary 
  materials 
  appear 
  to 
  reveal 
  

   the 
  denudative 
  loss 
  of 
  radioactive 
  materials. 
  

  

  That 
  thorium 
  is 
  a 
  generally 
  distributed 
  constituent 
  of 
  the 
  

   earth's 
  crust 
  and 
  enters 
  into 
  the 
  composition 
  of 
  deep-seated 
  

   materials 
  seems 
  established 
  by 
  its 
  universal 
  presence 
  through- 
  

   out 
  so 
  vast 
  and 
  complex 
  a 
  region 
  as 
  that 
  traversed 
  by 
  the 
  

   Al|)ine 
  tunnel, 
  as 
  well 
  as 
  by 
  its 
  presence 
  in 
  plutonic 
  rocks 
  

   and 
  lavas 
  of 
  many 
  ages 
  and 
  from 
  many 
  parts 
  of 
  the 
  world, 
  

   and 
  in 
  the 
  waters 
  and 
  sediments 
  of 
  the 
  ocean. 
  

  

  Trinity 
  College, 
  May 
  22. 
  

  

  * 
  I 
  desire, 
  here, 
  to 
  correct 
  a 
  mistake 
  into 
  which 
  I 
  fell 
  when 
  referring- 
  in 
  

   my 
  previous 
  paper 
  to 
  the 
  views 
  of 
  Professor 
  Soddy. 
  A 
  misinterpretation 
  

   of'a 
  passage 
  in 
  his 
  paper 
  of 
  Phil. 
  Mag. 
  Oct. 
  1908,' 
  led 
  me 
  to 
  believe 
  that 
  

   the 
  writer 
  maintained 
  the 
  probability 
  of 
  equality 
  between 
  the 
  rates 
  of 
  

   break 
  up 
  of 
  uranium 
  and 
  thorium. 
  I 
  have 
  Professor 
  Soddy's 
  authority 
  

   for 
  stating 
  that 
  he 
  had 
  not 
  intended 
  to 
  express 
  that 
  view. 
  

  

  Phil. 
  Marj, 
  S. 
  6. 
  Vol. 
  18. 
  No. 
  103. 
  Julu 
  1909, 
  L 
  

  

  