﻿OLDEK 
  ALLUVIUM. 
  47 
  

  

  evidence 
  afforded 
  by 
  the 
  entire 
  absence, 
  as 
  far 
  as 
  my 
  knowledge 
  goes, 
  of 
  

   fluviatile 
  and 
  terrestrial 
  mollusca 
  from 
  the 
  older 
  alluvial 
  clay, 
  — 
  a 
  deposit 
  

   which 
  seems 
  peculiarly 
  fitted 
  for 
  their 
  perfect 
  preservation 
  ; 
  and 
  %ndly— 
  

   the 
  physical 
  argument 
  which 
  exists 
  in 
  the 
  complete 
  homogeneity 
  of 
  the 
  

   entire 
  deposit, 
  which 
  seems 
  strongly 
  to 
  militate 
  against 
  the 
  idea 
  of 
  its 
  

   being 
  the 
  result 
  of 
  river 
  action. 
  

  

  With 
  regard 
  to 
  the 
  1st 
  argument, 
  I 
  am 
  aware 
  of 
  the 
  disfavor 
  with 
  

   which 
  mere 
  negative 
  evidence 
  is 
  regarded, 
  but 
  it 
  is 
  not 
  therefore 
  to 
  be 
  

   altogether 
  neglected. 
  In 
  the 
  Narbada 
  valley 
  we 
  find 
  a 
  clay 
  not 
  greatly 
  

   dissimilar 
  from 
  the 
  older 
  alluvium 
  of 
  Bengal, 
  and 
  usually 
  devoid 
  of 
  organic 
  

   remains. 
  At 
  some 
  spots, 
  however, 
  it 
  contains 
  land 
  shells 
  and 
  mammalian 
  

   bones 
  (vide 
  Memoirs 
  of 
  the 
  Geological 
  Survey 
  of 
  India, 
  Vol. 
  II, 
  p. 
  279), 
  

   and 
  what 
  is 
  more 
  important, 
  two 
  or 
  three 
  species 
  of 
  Unio 
  with 
  valves 
  united 
  

   and 
  in 
  the 
  position 
  they 
  occupied 
  in 
  the 
  clay 
  during 
  life. 
  Now, 
  neither 
  

   in 
  Bengal 
  nor 
  Pegu 
  have 
  any 
  similar 
  remains 
  of 
  freshwater 
  Pelecypoda 
  

   been 
  found, 
  though 
  the 
  conditions 
  for 
  their 
  preservation 
  are 
  very 
  similar 
  

   to 
  those 
  which 
  are 
  present 
  in 
  the 
  Narbada 
  valley 
  ; 
  and 
  unless 
  we 
  suppose 
  

   which 
  I 
  am 
  not 
  prepared 
  to 
  admit, 
  that 
  a 
  less 
  careful 
  and 
  anxious 
  

   search 
  for 
  fossils 
  has 
  been 
  made 
  in 
  Bengal 
  and 
  Pegu 
  than 
  was 
  made 
  in 
  

   the 
  Narbada 
  district, 
  it 
  is 
  not 
  easy 
  to 
  account 
  for 
  this 
  almost 
  total 
  

   absence 
  of 
  organic 
  remains 
  if 
  the 
  conditions 
  of 
  deposition 
  were 
  identical. 
  

   The 
  presence 
  of 
  either 
  land 
  or 
  freshwater 
  Gasteropoda 
  would 
  certainly 
  not 
  

   prove 
  the 
  freshwater 
  character 
  of 
  the 
  deposit, 
  as 
  such 
  are 
  found 
  in 
  

   undeniably 
  marine 
  beds 
  ; 
  but 
  the 
  evidence 
  of 
  any 
  species 
  of 
  Unio 
  having 
  

   occupied 
  the 
  clay 
  in 
  a 
  living 
  state 
  is 
  indisputable; 
  and 
  this 
  simple 
  

   evidence 
  of 
  the 
  lacustrine 
  nature 
  and 
  origin 
  of 
  the 
  older 
  alluvium 
  is, 
  as 
  

   far 
  as 
  I 
  am 
  aware, 
  totally 
  wanting. 
  

  

  The 
  second 
  or 
  physical 
  argument 
  against 
  the 
  fluviatile 
  origin 
  of 
  

   the 
  clay 
  is 
  perhaps 
  stronger 
  than 
  the 
  last. 
  It 
  has 
  been 
  argued 
  that 
  the 
  

   homogeneity 
  of 
  a 
  deposit 
  like 
  that 
  I 
  am 
  describing 
  may 
  be 
  the 
  result 
  of 
  

   the 
  extremely 
  small 
  increments 
  of 
  sediment 
  by 
  which 
  it 
  has 
  been 
  built 
  

  

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