﻿THE 
  TERTIARY 
  FORMATIONS 
  OF 
  VIRGINIA. 
  327 
  

  

  six 
  feet 
  by 
  a 
  brownish 
  yellow 
  sand, 
  intermixed 
  with 
  stripes 
  of 
  clay. 
  

   Beneath 
  this 
  is 
  a 
  thin 
  layer 
  of 
  about 
  one 
  foot, 
  of 
  very 
  argillaceous 
  and 
  

   ferruginous 
  clay 
  of 
  a 
  red 
  colour. 
  This 
  rests 
  upon 
  a 
  few 
  inches 
  

   thickness 
  of 
  gravel, 
  consisting 
  of 
  water-worn 
  quartz, 
  rarely 
  larger 
  than 
  

   a 
  pea. 
  Beneath 
  this 
  is 
  a 
  layer, 
  from 
  one 
  to 
  two 
  feet 
  thick, 
  consisting 
  

   of 
  yellow 
  sand, 
  containing 
  a 
  great 
  deal 
  of 
  the 
  green 
  or 
  chloritic 
  sand? 
  

   arranged 
  in 
  narrow 
  r 
  stripes. 
  Next 
  follows 
  a 
  layer 
  of 
  the 
  same 
  sand, 
  con- 
  

   taining 
  principally 
  Chama 
  and 
  Venus 
  deformis. 
  This 
  is 
  from 
  two 
  to 
  three 
  

   feet 
  in 
  thickness. 
  Immediately 
  below 
  is 
  a 
  stratum 
  consisting 
  almost 
  ex- 
  

   clusively 
  of 
  Chama, 
  with 
  a 
  few 
  7 
  Area 
  centenaria, 
  &c. 
  This 
  stratum, 
  vary- 
  

   ing 
  from 
  three 
  to 
  four 
  feet 
  in 
  thickness, 
  is 
  a 
  mass 
  of 
  compacted 
  shells, 
  with 
  

   but 
  little 
  earthy 
  matter 
  intervening. 
  The 
  earthy 
  matter 
  contains 
  a 
  very 
  

   large 
  proportion 
  of 
  the 
  chloritic 
  sand. 
  The 
  next 
  stratum 
  is 
  composed 
  

   chiefly 
  of 
  large 
  Pectens, 
  and 
  has 
  a 
  thickness 
  of 
  from 
  one 
  to 
  two 
  feet. 
  

   Below 
  this 
  is 
  another 
  dense 
  stratum 
  of 
  Chama, 
  together 
  with 
  Area 
  cen- 
  

   tenaria, 
  Panopea 
  reflexa, 
  &c, 
  and 
  also 
  very 
  rich 
  in 
  the 
  green 
  sand. 
  Thick- 
  

   ness, 
  from 
  four 
  to 
  six 
  feet. 
  Then 
  follows 
  a 
  second 
  layer 
  containing 
  

   Pectens 
  with 
  Ostrea 
  compressirostra, 
  one 
  foot 
  in 
  thickness. 
  A 
  third 
  

   stratum, 
  in 
  which 
  Chama 
  predominates, 
  follows 
  next, 
  in 
  thickness 
  from 
  

   two 
  to 
  three 
  feet, 
  and 
  at 
  the 
  base 
  of 
  the 
  cliff 
  is 
  a 
  layer 
  containing 
  Pec- 
  

   tens, 
  Ostrea 
  compressirostra, 
  &c, 
  four 
  to 
  five 
  feet 
  in 
  thickness. 
  

  

  17. 
  Thus 
  through 
  a 
  height 
  of 
  more 
  than 
  twenty 
  feet 
  in 
  some 
  

   places, 
  the 
  cliff 
  consists 
  principally 
  of 
  shells, 
  of 
  which 
  there 
  are 
  a 
  great 
  

   many 
  species, 
  besides 
  those 
  mentioned 
  as 
  predominating 
  in 
  the 
  several 
  

   beds. 
  On 
  the 
  extensive 
  contiguous 
  estates 
  of 
  King's 
  Mill 
  and 
  Little- 
  

   town, 
  these 
  shells 
  are 
  largely 
  used 
  as 
  a 
  manure 
  : 
  and 
  for 
  this 
  pur- 
  

   pose 
  the 
  first 
  and 
  second 
  beds 
  of 
  Chama 
  are 
  preferred 
  on 
  account 
  of 
  

   the 
  immense 
  amount 
  of 
  calcareous 
  matter, 
  and 
  the 
  large 
  proportion 
  of 
  

   green 
  sand 
  which 
  they 
  contain. 
  Judging 
  from 
  the 
  occasional 
  appear- 
  

   ance 
  of 
  bluish 
  green-clay 
  on 
  the 
  line 
  of 
  the 
  beach, 
  and 
  in 
  some 
  places 
  

   immediately 
  at 
  the 
  base 
  of 
  the 
  cliff 
  just 
  described, 
  it 
  is 
  highly 
  probable 
  

   that 
  a 
  continuous 
  stratum 
  of 
  this 
  substance 
  lies 
  beneath 
  the 
  other 
  beds 
  

   throughout 
  the 
  whole 
  extent 
  observed. 
  A 
  horizontal 
  bed 
  of 
  yellow- 
  

   ish 
  clay 
  extends 
  for 
  some 
  distance 
  along 
  a 
  lower 
  portion 
  of 
  the 
  cliff, 
  in 
  

   which 
  there 
  are 
  no 
  fossils, 
  running 
  within 
  a 
  few 
  feet 
  of 
  its 
  upper 
  edge, 
  

   and 
  beneath 
  this 
  bed, 
  and 
  parallel 
  to 
  it, 
  is 
  a 
  thin 
  layer 
  of 
  the 
  iron 
  ore 
  

  

  