﻿FOSSIL-WOOD 
  GROUP. 
  

  

  65 
  

  

  Next 
  to 
  the 
  abundance 
  of 
  fossil-wood 
  in 
  this 
  bed, 
  its 
  most 
  marked 
  

   peculiarity 
  is 
  the 
  quantity 
  of 
  the 
  hydrated 
  peroxide 
  of 
  iron 
  it 
  con- 
  

   tains 
  in 
  the 
  form 
  of 
  concretions, 
  in 
  places 
  so 
  abundant 
  as 
  to 
  have 
  

   formerly 
  served 
  for 
  the 
  manufacture 
  of 
  iron, 
  which 
  was 
  once 
  largely 
  

   carried 
  on 
  within 
  the 
  area 
  occupied 
  by 
  this 
  group 
  of 
  beds, 
  especially 
  

   in 
  the 
  neighbourhood 
  of 
  the 
  villages 
  of 
  Shuaybandor, 
  Kiungalay 
  and 
  

   Yaybor. 
  The 
  ore 
  occurs 
  occasionally 
  as 
  a 
  band 
  of 
  about 
  three 
  inches 
  

   in 
  thickness, 
  but 
  more 
  usually 
  in 
  the 
  form- 
  of 
  variously 
  shaped 
  concretions 
  

   one 
  to 
  four 
  inches 
  in 
  length. 
  In 
  the 
  upper 
  sand 
  these 
  concretions 
  are 
  

   regular 
  and 
  symmetrically 
  shaped, 
  amygdaloidal, 
  spherical, 
  cubical, 
  

   cylindrical, 
  with 
  both 
  round 
  and 
  truncated 
  ends, 
  discoidal, 
  &c. 
  ; 
  and 
  all 
  

   these 
  forms 
  are 
  clearly 
  the 
  result 
  of 
  segregative 
  action 
  in 
  the 
  recently 
  

   deposited 
  materials. 
  Of 
  whatever 
  shape, 
  however, 
  the 
  concretions 
  are- 
  

   all 
  very 
  similar 
  in 
  structure, 
  consisting 
  of 
  an 
  external 
  crust 
  of 
  concen- 
  

   trie 
  layers 
  of 
  brown 
  haematite, 
  surrounding 
  a 
  kernel 
  of 
  pure 
  white 
  or 
  

   yellowish 
  clay, 
  lying 
  loose 
  and 
  shrunken 
  as 
  it 
  were 
  in 
  the 
  interior. 
  

   Externally 
  these 
  nodular 
  concretions 
  are 
  roughened 
  through 
  the 
  adhe- 
  

   sion 
  of 
  sand 
  ; 
  but 
  a 
  slight 
  tap 
  causes 
  the 
  rough 
  crust 
  to 
  scale 
  off, 
  leaving 
  

   a 
  perfectly 
  smooth 
  surface. 
  Internally 
  these 
  nodules 
  often 
  present 
  a 
  

   blistered 
  surface, 
  from 
  the 
  mammillary 
  crystallization 
  of 
  limonite. 
  

   In 
  some 
  of 
  the 
  coarse 
  beds 
  of 
  the 
  group, 
  where 
  the 
  harsh 
  charac- 
  

   ter 
  of 
  the 
  rock 
  has 
  interfered 
  with 
  the 
  regular 
  segregation 
  of 
  the 
  

   mineral, 
  irregular 
  seams 
  or 
  shrinkage-fissures 
  are 
  seen 
  lined 
  by 
  it 
  (limo- 
  

   nite), 
  which 
  on 
  the 
  weathered 
  surface 
  impart 
  a 
  pseudo-slaggy 
  appearance 
  

   to 
  the 
  sandstone. 
  In 
  some 
  rare 
  instances 
  the 
  segregation 
  of 
  this 
  min- 
  

   eral 
  would 
  seem 
  to 
  have 
  given 
  rise 
  to 
  a 
  botryoidal 
  structure 
  in 
  the 
  sand- 
  

   stone, 
  manganese 
  being 
  then 
  present. 
  

  

  Associated 
  with 
  this 
  sand 
  and 
  forming 
  irregular 
  courses 
  in 
  it, 
  more 
  

  

  or 
  less 
  lenticularly 
  arranged, 
  occur 
  some 
  hard 
  sandstones, 
  sometimes 
  very 
  

  

  fine-grained, 
  at 
  others 
  a 
  pebbly 
  grit 
  or 
  even 
  coarse 
  conglomerate. 
  No 
  

  

  regular 
  position 
  can 
  be 
  assigned 
  in 
  the 
  sand 
  to 
  these 
  subordinate 
  layers; 
  

  

  I 
  : 
  ( 
  253 
  ) 
  

  

  