﻿34 
  BOSE 
  : 
  GEOLOGY 
  OP 
  THE 
  LOWER 
  NARBADA 
  VALLEY. 
  

  

  The 
  non-intervention 
  of 
  the 
  oyster 
  zone 
  at 
  places 
  between 
  the 
  Nimar 
  

   sandstone 
  and 
  the 
  nodular 
  limestone 
  may 
  be 
  due 
  to 
  denudation 
  of 
  the 
  

   former 
  previous 
  to 
  the 
  deposition 
  of 
  the 
  latter 
  ; 
  and, 
  if 
  so, 
  the 
  ease 
  would 
  

   be 
  one 
  of 
  slight 
  unconformity. 
  But 
  the 
  absence 
  of 
  the 
  oysters 
  may 
  be 
  

   due 
  to 
  local 
  causes 
  ; 
  and 
  in 
  this 
  more 
  probable 
  case 
  the 
  beds 
  in 
  ques- 
  

   tion 
  would 
  be 
  considered 
  to 
  pass 
  into 
  the 
  overlying 
  limestones 
  without 
  

   any 
  observable 
  break. 
  Nevertheless, 
  the 
  fact 
  that 
  the 
  latter 
  differ 
  so 
  

   remarkably 
  from 
  the 
  former 
  lithologically 
  implies 
  no 
  inconsiderable 
  lapse 
  

   of 
  time. 
  

  

  It 
  may 
  seem 
  ridiculous 
  to 
  attempt 
  to 
  fix 
  the 
  age 
  of 
  a 
  deposit, 
  with 
  

   any 
  approach 
  to 
  precision, 
  on 
  the 
  approximate 
  identification 
  of 
  only 
  

   one 
  fossil, 
  and 
  that, 
  too, 
  merely 
  an 
  oyster. 
  But 
  this 
  bivalve 
  is 
  a 
  

   very 
  characteristic 
  fossil 
  of 
  the 
  deposits 
  under 
  consideration 
  ; 
  and 
  if 
  it 
  

   passes 
  up 
  to 
  the 
  overlying 
  limestone, 
  as 
  it 
  does 
  at 
  Ghatia 
  and 
  south 
  of 
  

   Kawant, 
  it 
  does 
  so 
  in 
  considerably 
  diminished 
  numbers, 
  and, 
  as 
  a 
  rule, 
  in 
  

   diminutive 
  forms, 
  and 
  dies 
  out 
  in 
  the 
  course 
  of 
  deposition. 
  Now, 
  the 
  

   nodular 
  limestone, 
  which 
  contains 
  a 
  well-defined 
  marine 
  fauna, 
  will 
  

   be 
  shown 
  in 
  the 
  next 
  chapter 
  to 
  be 
  on 
  the 
  same 
  horizon 
  as 
  the 
  gault 
  or 
  

   albian 
  of 
  the 
  European 
  cretaceous 
  system. 
  We 
  may 
  therefore 
  ascribe 
  

   the 
  oyster-bearing 
  beds, 
  not 
  without 
  some 
  show 
  of 
  probability, 
  to 
  a 
  lower 
  

   (neocomian) 
  horizon. 
  The 
  oyster 
  being 
  closely 
  allied 
  to 
  an 
  European 
  

   neocomian 
  form 
  adds 
  strength 
  to 
  the 
  supposition. 
  

  

  Age 
  of 
  Nimdr 
  sandstone. 
  — 
  With 
  regard 
  to 
  the 
  age 
  of 
  the 
  sandstone 
  

   underlying 
  the 
  oyster 
  beds 
  (the 
  Nimar 
  sandstone) 
  , 
  it 
  is 
  perhaps 
  pre- 
  

   mature 
  to 
  say 
  anything 
  at 
  present, 
  considering 
  that 
  the 
  western 
  portion 
  

   of 
  the 
  lower 
  Narbada 
  valley, 
  where 
  it 
  is 
  best 
  developed, 
  1 
  has 
  not 
  yet 
  

   been 
  examined 
  in 
  detail. 
  The 
  lithological 
  dissimilarity 
  between 
  the 
  

   fine-grained, 
  thin-bedded 
  upper 
  strata 
  and 
  the 
  coarse 
  conglomeratic 
  

   deposits 
  in 
  which 
  the 
  oysters 
  occur 
  is 
  great. 
  But 
  wherever 
  the 
  two 
  

   groups 
  are 
  found 
  together, 
  there 
  is 
  perfect 
  conformity 
  between 
  them 
  ; 
  it 
  

   is 
  therefore 
  highly 
  probable 
  that 
  they 
  are 
  both 
  of 
  lower 
  cretaceous 
  age. 
  

   Some 
  light 
  will 
  be 
  thrown 
  on 
  the 
  question 
  when 
  the 
  affinities 
  of 
  the 
  

  

  ( 
  31 
  ) 
  

  

  Manual," 
  p. 
  295 
  j 
  " 
  Memoirs," 
  VI, 
  pt. 
  3, 
  pp. 
  145—185. 
  

  

  