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  CONTRIBUTIONS 
  TO 
  THE 
  GEOLOGY 
  OF 
  

  

  is 
  composed 
  principally 
  of 
  Chama 
  congregata. 
  In 
  many 
  localities 
  also, 
  

   the 
  large 
  Pectens 
  mingled 
  with 
  Ostrea 
  Virginica 
  occupy 
  the 
  highest 
  place. 
  

   But 
  generally, 
  the 
  same 
  shell 
  reappears 
  as 
  a 
  predominant 
  constituent 
  

   of 
  one 
  or 
  more 
  of 
  the 
  subjacent 
  beds 
  ; 
  and 
  such 
  is 
  the 
  diversity 
  of 
  ar- 
  

   rangement, 
  even 
  in 
  places 
  but 
  a 
  few 
  miles 
  distant, 
  that 
  it 
  is 
  obvious 
  

   that 
  no 
  general 
  order 
  of 
  succession 
  exists. 
  Thus 
  in 
  a 
  range 
  of 
  three 
  

   miles 
  we 
  fiud 
  Perna 
  maxillata 
  in 
  some 
  localities 
  in 
  the 
  lowest 
  stratum 
  

   of 
  dark 
  blue 
  argillaceous 
  sand 
  ; 
  in 
  others, 
  forming 
  an 
  upper 
  or 
  even 
  the 
  

   highest 
  layer 
  of 
  the 
  series. 
  At 
  Waller's 
  Mill, 
  three 
  miles 
  from 
  Wil- 
  

   liamsburg, 
  this 
  fossil 
  overlies 
  the 
  other 
  shells 
  ; 
  whereas 
  at 
  the 
  College 
  

   Mill, 
  as 
  already 
  stated, 
  it 
  forms 
  a 
  part 
  of 
  the 
  lowest 
  visible 
  stratum. 
  

   So 
  far, 
  therefore, 
  as 
  relates 
  to 
  the 
  tertiary 
  beds 
  of 
  the 
  district 
  of 
  which 
  we 
  

   are 
  now 
  treating, 
  and 
  indeed 
  of 
  Virginia 
  generally, 
  there 
  is 
  no 
  such 
  

   constancy 
  in 
  the 
  position 
  of 
  this 
  fossil 
  in 
  the 
  series, 
  as 
  to 
  warrant 
  the 
  

   theoretical 
  inference 
  of 
  its 
  belonging 
  to 
  a 
  different 
  tertiary 
  period, 
  de- 
  

   duced 
  by 
  Mr 
  Conrad 
  from 
  its 
  relation 
  to 
  the 
  other 
  tertiary 
  fossils 
  in 
  

   certain 
  districts 
  in 
  Maryland. 
  

  

  14. 
  With 
  the 
  view 
  of 
  conveying 
  more, 
  precise 
  ideas 
  of 
  the 
  disposi- 
  

   tion 
  of 
  the 
  fossils 
  in 
  this 
  region, 
  as 
  well 
  as 
  describing 
  some 
  interesting 
  

   facts 
  peculiar 
  to 
  certain 
  districts 
  which 
  have 
  been 
  investigated, 
  we 
  an- 
  

   nex 
  the 
  following 
  details 
  in 
  relation 
  to 
  some 
  of 
  the 
  more 
  important 
  

   localities. 
  

  

  1 
  5. 
  King's 
  Mill, 
  one 
  of 
  the 
  most 
  interesting 
  fossil 
  localities 
  in 
  the 
  

   neighbourhood 
  of 
  Williamsburg, 
  is 
  situated 
  on 
  the 
  north 
  bank 
  of 
  the 
  

   James 
  river, 
  about 
  twenty-five 
  miles 
  from 
  its 
  mouth. 
  The 
  cliff 
  in 
  which 
  

   the 
  shells 
  appear 
  is 
  abrupt, 
  and 
  has 
  a 
  height 
  varying 
  from 
  twenty 
  to 
  

   forty-five 
  feet 
  above 
  the 
  water. 
  The 
  strata 
  of 
  shells 
  extend 
  along 
  the 
  

   river 
  with 
  slight 
  interruptions, 
  when 
  the 
  cliff 
  sinks 
  nearly 
  to 
  the 
  level 
  

   of 
  the 
  water, 
  for 
  a 
  distance 
  of 
  between 
  two 
  and 
  three 
  miles, 
  and 
  they 
  

   are 
  found 
  in 
  a 
  somewhat 
  similar 
  order 
  of 
  superposition 
  for 
  some 
  dis- 
  

   tance 
  inland. 
  Their 
  general 
  direction 
  is 
  horizontal," 
  but 
  the 
  outline 
  of 
  

   any 
  one 
  stratum 
  is 
  frequently 
  very 
  irregular, 
  the 
  surface 
  rising 
  and 
  

   falling 
  with 
  a 
  steep 
  inclination. 
  This 
  irregular 
  outline 
  is 
  particularly 
  

   remarkable 
  with 
  the 
  beds 
  of 
  Chama, 
  which 
  are 
  very 
  thick 
  at 
  some 
  

   points, 
  and 
  then 
  fine 
  out 
  rapidly 
  and 
  again 
  expand. 
  

  

  16. 
  This 
  deposit 
  of 
  shells 
  is 
  covered 
  to 
  the 
  depth 
  of 
  from 
  four 
  to 
  

  

  