﻿THE 
  TERTIARY 
  FORMATIONS 
  OF 
  VIRGINIA. 
  321 
  

  

  5. 
  A 
  thin 
  stratum 
  of 
  red 
  ferruginous 
  stone, 
  containing 
  a 
  large 
  pro- 
  

   portion 
  of 
  oxide 
  of 
  iron, 
  is 
  found 
  in 
  this 
  region, 
  running 
  horizontally 
  

   below 
  the 
  beds 
  of 
  clay 
  before 
  described, 
  and 
  generally 
  separated 
  by 
  

   only 
  a 
  few 
  feet 
  from 
  the 
  underlying 
  masses 
  of 
  shells. 
  This 
  stratum, 
  

   which 
  is 
  very 
  generally 
  present, 
  varies 
  in 
  thickness 
  from 
  an 
  inch 
  to 
  a 
  

   foot. 
  Its 
  texture 
  is 
  sometimes 
  cellular, 
  sometimes 
  compact 
  and 
  fibrous, 
  

   like 
  that 
  of 
  certain 
  varieties 
  of 
  hematite. 
  

  

  6. 
  The 
  matter, 
  which, 
  in 
  most 
  cases, 
  rests 
  immediately 
  upon 
  the 
  

   shells, 
  is 
  a 
  yellowish 
  brown 
  sand, 
  frequently 
  containing 
  a 
  large 
  pro- 
  

   portion 
  of 
  clay. 
  Throughout 
  this 
  mass, 
  and 
  often 
  extending 
  to 
  the 
  

   distance 
  of 
  five 
  or 
  six 
  feet 
  from 
  the 
  shells, 
  particles 
  of 
  green 
  sand, 
  or 
  

   the 
  silicate 
  of 
  iron 
  and 
  potash, 
  are 
  more 
  or 
  less 
  abundantly 
  dissemi- 
  

   nated, 
  and 
  in 
  the 
  immediate 
  vicinity 
  of 
  the 
  shells 
  these 
  particles 
  are 
  

   generally 
  condensed 
  into 
  narrow 
  stripes, 
  conforming 
  in 
  flexure 
  to 
  the 
  

   irregularities 
  of 
  the 
  bed 
  beneath. 
  Even 
  where 
  a 
  deep 
  hole 
  exists 
  in 
  the 
  

   layer 
  of 
  shells, 
  the 
  stripes 
  of 
  green 
  sand 
  are 
  seen 
  still 
  following 
  the 
  

   depression 
  and 
  rise 
  of 
  the 
  surface, 
  and 
  preserving 
  a 
  uniform 
  distance 
  

   from 
  it. 
  Sometimes 
  these 
  thin 
  layers 
  are 
  so 
  much 
  indurated 
  as 
  to 
  

   have 
  almost 
  the 
  appearance 
  of 
  stone. 
  In 
  none 
  of 
  the 
  strata 
  above 
  de- 
  

   scribed 
  have 
  fossils 
  of 
  any 
  description 
  ever 
  been 
  discovered. 
  

  

  7. 
  The 
  materials 
  with 
  which 
  the 
  shells 
  are 
  intermixed, 
  or 
  in 
  which 
  

   they 
  are 
  embedded, 
  have 
  various 
  characters. 
  In 
  some 
  cases 
  they 
  

   consist 
  principally 
  of 
  a 
  nearly 
  white 
  sand 
  ; 
  in 
  others 
  the 
  argillaceous 
  

   matter 
  greatly 
  predominates, 
  and 
  the 
  mass 
  is 
  a 
  somewhat 
  tenacious 
  

   clay. 
  Frequently 
  much 
  oxide 
  of 
  iron 
  is 
  mingled 
  with 
  the 
  earthy 
  

   matter, 
  giving 
  it 
  more 
  or 
  less 
  of 
  a 
  yellow 
  or 
  brown 
  appearance, 
  and 
  

   this 
  is 
  the 
  aspect 
  which 
  the 
  upper 
  beds 
  containing 
  shells 
  most 
  usually 
  

   present. 
  Very 
  generally 
  the 
  lowest 
  visible 
  fossiliferous 
  stratum 
  is 
  

   composed 
  of 
  a 
  green 
  silicious 
  sand, 
  and 
  a 
  bluish 
  clay, 
  which 
  being 
  

   always 
  very 
  moist, 
  is 
  soft 
  and 
  tenacious, 
  and 
  presents 
  a 
  dark 
  blue 
  or 
  

   black 
  colour. 
  At 
  the 
  base 
  of 
  the 
  cliffs 
  on 
  the 
  James 
  and 
  York 
  rivers, 
  

   this 
  stratum 
  may 
  be 
  traced 
  continuously 
  for 
  considerable 
  distances, 
  

   rarely 
  rising 
  more 
  than 
  two 
  or 
  three 
  feet 
  above 
  the 
  level 
  of 
  the 
  water, 
  

   and 
  presenting 
  an 
  even 
  horizontal 
  outline. 
  In 
  the 
  deep 
  ravines, 
  and 
  

   low 
  down 
  in 
  the 
  banks 
  of 
  shells, 
  generally, 
  throughout 
  this 
  region, 
  a 
  

  

  vol. 
  v. 
  — 
  4 
  F 
  

  

  