﻿OLDER 
  ALLUVIUM. 
  55 
  

  

  after 
  some 
  years' 
  search, 
  that 
  I 
  found 
  a 
  bed 
  of 
  precisely 
  the 
  character 
  of 
  

   some 
  of 
  the 
  hardest 
  and 
  most 
  peculiar 
  of 
  the 
  silicious 
  rocks 
  of 
  this 
  

   bed. 
  The 
  hill 
  of 
  Yethaydoung 
  is 
  situated 
  between 
  the 
  Maday 
  and 
  

   Thanni 
  streams, 
  very 
  steep 
  and 
  in 
  part 
  completely 
  scarped. 
  It 
  con- 
  

   sists 
  of 
  a 
  harsh 
  sandstone 
  belonging 
  to 
  the 
  Triassie 
  rocks 
  ; 
  but 
  on 
  the 
  

   crest 
  of 
  the 
  hill 
  this 
  sandstone 
  is 
  intensely 
  altered, 
  so 
  as 
  to 
  assume 
  

   the 
  appearance 
  of 
  a 
  harsh 
  quartzite. 
  Where 
  this 
  induration 
  is 
  most 
  

   displayed 
  the 
  rock 
  is 
  broken 
  up, 
  brecciated, 
  and 
  much 
  seamed 
  by 
  thin 
  

   veins 
  of 
  quartz. 
  The 
  colour 
  of 
  the 
  hardest 
  and 
  most 
  altered 
  portions 
  

   is 
  brown 
  or 
  yellowish-brown, 
  with 
  little 
  vuggy 
  cavities 
  lined 
  with 
  small 
  

   quartz 
  crystals. 
  This 
  rock 
  might 
  easily 
  be 
  set 
  down 
  as 
  a 
  vein-stone, 
  if 
  

   judged 
  from 
  a 
  small 
  specimen 
  ; 
  but 
  it 
  is 
  seen 
  to 
  be 
  merely 
  a 
  local 
  altera- 
  

   tion 
  of 
  one 
  of 
  the 
  silicious 
  beds 
  of 
  the 
  Triassie 
  group 
  ; 
  though 
  what 
  can 
  

   be 
  the 
  cause 
  of 
  the 
  appearance 
  produced 
  is 
  far 
  from 
  clear. 
  The 
  most 
  

   probable 
  explanation 
  that 
  suggested 
  itself 
  to 
  me 
  on 
  the 
  ground 
  was 
  that 
  

   the 
  baking 
  and 
  breeciation 
  of 
  the 
  rock 
  was 
  produced 
  by 
  the 
  passage 
  of 
  

   a 
  dyke 
  of 
  serpentine, 
  directly 
  under 
  the 
  hill, 
  the 
  position 
  being 
  not 
  very 
  

   far 
  out 
  of 
  the 
  line 
  connecting 
  a 
  long 
  dyke 
  of 
  serpentine 
  North 
  of 
  it 
  

   with 
  the 
  mass 
  of 
  Nattoung 
  serpentine 
  to 
  the 
  South. 
  One 
  thing 
  is 
  certain 
  

   that 
  from 
  local 
  sources, 
  such 
  as 
  Yethaydoung 
  hill, 
  and 
  other 
  spots 
  within 
  

   the 
  boundary 
  of 
  the 
  Triassie, 
  and 
  other 
  altered 
  rocks 
  of 
  the 
  Arakan 
  

   Yomah, 
  the 
  bulk 
  of 
  the 
  coarse 
  gravel 
  and 
  boulders 
  strewed 
  over 
  the 
  

   Western 
  portion 
  of 
  the 
  Irrawadi 
  valley 
  must 
  have 
  been 
  derived. 
  I 
  have 
  

   already 
  stated 
  my 
  conviction 
  that 
  mere 
  river 
  action 
  is 
  inadequate 
  to 
  

   account 
  for 
  the 
  formation 
  of 
  much 
  of 
  the 
  shingle 
  and 
  boulders 
  found 
  in 
  

   the 
  Irrawadi 
  gravel, 
  and 
  inadequate 
  also 
  to 
  their 
  transport, 
  marine 
  action 
  

   being 
  the 
  only 
  alternative, 
  and 
  one 
  which 
  seems 
  precisely 
  to 
  meet 
  the 
  

   conditions 
  present. 
  

  

  Along 
  the 
  skirts 
  of 
  the 
  Pegu 
  Yomah 
  a 
  broad 
  belt 
  of 
  sandy 
  deposits 
  

   occurs, 
  lateritic 
  in 
  places, 
  occupying 
  the 
  position 
  of, 
  and 
  replacing 
  the 
  

   coarser 
  gravels 
  to 
  the 
  Westward. 
  These 
  sandy 
  accumulations 
  acquire 
  

  

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