﻿vol. 
  53.] 
  on 
  rocks 
  from 
  the 
  baluchistan 
  border. 
  307 
  

  

  Discussion. 
  

  

  The 
  President 
  commented 
  on 
  the 
  advantage 
  of 
  heredity 
  in 
  taste, 
  

   and 
  on 
  the 
  excellent 
  observations 
  made 
  by 
  Capt. 
  McMahon, 
  as 
  well 
  

   as 
  the 
  valuable 
  information 
  which 
  he 
  had 
  brought 
  back. 
  Con- 
  

   cerning 
  the 
  corrosion 
  of 
  basic 
  minerals 
  by 
  silica, 
  he 
  observed 
  that 
  

   silica 
  might 
  be 
  truly 
  a 
  corrosive 
  mineral, 
  but 
  hitherto 
  the 
  idea 
  had 
  

   been 
  that 
  the 
  basic 
  mineral 
  had 
  decomposed 
  in 
  situ, 
  and 
  that 
  the 
  

   silica 
  had 
  filled 
  up 
  the 
  hollows 
  and 
  cracks 
  resulting 
  from 
  this 
  

   decomposition. 
  It 
  was 
  perhaps 
  a 
  general 
  mistake 
  to 
  suppose 
  that 
  

   faults 
  always 
  run 
  along 
  valleys. 
  Faults 
  may 
  often 
  be 
  indicated 
  by 
  

   valleys, 
  but 
  in 
  many 
  parts 
  of 
  the 
  country 
  they 
  run 
  across 
  the 
  ridges 
  

   as 
  well. 
  

  

  Mr. 
  Griesbach 
  considered 
  the 
  paper 
  just 
  read 
  a 
  valuable 
  contribu- 
  

   tion 
  to 
  our 
  knowledge 
  of 
  Baluchistan. 
  But, 
  having 
  spent 
  some 
  years 
  

   in 
  that 
  part 
  of 
  Asia 
  himself, 
  he 
  wished 
  to 
  point 
  out 
  that 
  there 
  is 
  

   abundant 
  evidence 
  to 
  show 
  that 
  the 
  Pliocene 
  deposits 
  which 
  are 
  

   seen 
  in 
  Shorawak 
  and 
  the 
  neighbouring 
  Registan 
  have 
  not 
  been 
  laid 
  

   down 
  in 
  a 
  lake-basin, 
  but 
  are 
  chiefly 
  of 
  a 
  fluviatile 
  nature. 
  The 
  range 
  

   of 
  hills, 
  of 
  which 
  the 
  northern 
  portion 
  is 
  known 
  as 
  the 
  Koh-i-Khwaja 
  

   Amran, 
  is 
  composed 
  mostly 
  of 
  rocks 
  belonging 
  to 
  the 
  later 
  Cretaceous 
  

   and 
  Nummulitic 
  formations, 
  with 
  great 
  masses 
  of 
  intrusive 
  igneous 
  

   rocks. 
  Of 
  these 
  latter 
  the 
  peak 
  of 
  Khwaja 
  Amran 
  is 
  the 
  nucleus, 
  and 
  

   represents 
  a 
  remarkable 
  series 
  of 
  acid 
  rocks, 
  followed 
  by 
  ' 
  Nachschube 
  ' 
  

   of 
  basic 
  rocks. 
  The 
  long 
  fault-line 
  or 
  ' 
  earthquake-crack 
  ' 
  does 
  not, 
  

   however, 
  mark 
  the 
  boundary-line 
  between 
  sedimentary 
  and 
  igneous 
  

   rocks 
  in 
  that 
  part 
  of 
  the 
  world. 
  Quite 
  close 
  to 
  the 
  line 
  of 
  fault, 
  west 
  

   of 
  Chaman, 
  Hippuritic 
  Limestone 
  may 
  be 
  seen 
  in 
  situ 
  ; 
  and 
  rocks 
  of 
  

   Cretaceous 
  and 
  Tertiary 
  age 
  form 
  great 
  mountain-chains 
  north-east 
  of 
  

   Chaman 
  and 
  west 
  of 
  the 
  ' 
  earthquake-crack/ 
  It 
  is 
  questioned 
  whether 
  

   there 
  is 
  any 
  foundation 
  of 
  truth 
  for 
  the 
  rumoured 
  existence 
  of 
  

   actual 
  recent 
  craters 
  in 
  the 
  desert 
  west 
  of 
  the 
  Koh-i-Sultan. 
  Nearly 
  

   all 
  the 
  ridges 
  and 
  peaks 
  of 
  volcanic 
  rocks 
  in 
  this 
  Baluchi 
  desert 
  are 
  

   due 
  to 
  their 
  having 
  been 
  laid 
  bare 
  by 
  the 
  decomposition 
  and 
  removal 
  

   of 
  the 
  softer 
  sedimentary 
  strata 
  into 
  which 
  they 
  have 
  been 
  in- 
  

   truded. 
  

  

  Dr. 
  W. 
  T. 
  Blanford 
  congratulated 
  Capt. 
  McMahon 
  on 
  the 
  series 
  of 
  

   interesting 
  observations 
  brought 
  before 
  the 
  Society. 
  He 
  noticed 
  the 
  

   great 
  prevalence 
  of 
  Tertiary 
  and 
  Cretaceous 
  rocks 
  throughout 
  the 
  

   wide 
  area 
  extending 
  from 
  the 
  Indus 
  to 
  Mesopotamia. 
  The 
  volcanic 
  

   rocks 
  of 
  Eastern 
  Baluchistan, 
  like 
  the 
  Deccan 
  traps 
  of 
  India, 
  appear 
  

   to 
  be 
  of 
  Cretaceous 
  and 
  Lower 
  Eocene 
  age 
  ; 
  but 
  the 
  igneous 
  forma- 
  

   tions 
  near 
  the 
  Baluchistan 
  and 
  Persian 
  frontier 
  must 
  be, 
  in 
  part 
  at 
  

   all 
  events, 
  of 
  far 
  more 
  recent 
  origin, 
  some 
  of 
  the 
  cones 
  of 
  loose 
  

   materials 
  seen 
  by 
  the 
  speaker 
  between 
  Bampur 
  and 
  Bam 
  having 
  

   undergone 
  no 
  change 
  through 
  denudation. 
  Possibly 
  the 
  great 
  

   volcanic 
  eruptions 
  of 
  this 
  area 
  had 
  some 
  connexion 
  with 
  the 
  lateral 
  

   compression 
  of 
  the 
  rocks 
  in 
  Southern 
  Baluchistan, 
  Tertiary 
  rocks 
  

   being 
  found 
  vertical 
  or 
  nearly 
  so, 
  from 
  near 
  the 
  shores 
  of 
  the 
  Indian 
  

   Ocean 
  to 
  Jalk, 
  about 
  150 
  miles 
  across 
  the 
  strike. 
  The 
  remarkable 
  

  

  y2 
  

  

  