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  CONTRIBUTIONS 
  TO 
  THE 
  GEOLOGY 
  OF 
  

  

  the 
  beds 
  of 
  the 
  creeks 
  flowing 
  into 
  the 
  James 
  and 
  York 
  rivers. 
  The 
  

   system 
  of 
  ravines 
  connected 
  with 
  one 
  river, 
  are 
  separated 
  by 
  a 
  narrow 
  

   central 
  tract 
  from 
  those 
  connected 
  with 
  the 
  other, 
  and 
  in 
  a 
  general 
  

   view 
  of 
  the 
  district, 
  the 
  two 
  systems 
  present 
  the 
  appearance 
  of 
  mere 
  

   creeks 
  or 
  inlets, 
  subordinate 
  to 
  the 
  two 
  great 
  rivers 
  bounding 
  the 
  

   peninsula. 
  

  

  3. 
  The 
  superficial 
  stratum 
  of 
  the 
  region 
  we 
  are 
  describing 
  is 
  an 
  

   argillaceous 
  and 
  ferruginous 
  sand, 
  of 
  a 
  yellow, 
  and 
  sometimes 
  of 
  a 
  red- 
  

   dish 
  colour, 
  in 
  which 
  are 
  occasionally 
  found, 
  at 
  or 
  near 
  the 
  surface, 
  

   pebbles 
  and 
  small 
  boulders 
  of 
  sandstone, 
  rarely 
  as 
  much 
  as 
  six 
  inches 
  

   in 
  diameter. 
  The 
  nature 
  of 
  these 
  boulders 
  would 
  indicate 
  that 
  they 
  

   were 
  most 
  probably 
  derived 
  from 
  the 
  sandstone 
  formation 
  which 
  

   ranges 
  along 
  the 
  eastern 
  boundary 
  of 
  the 
  primary 
  ridge. 
  In 
  some 
  

   places 
  this 
  stratum 
  consists 
  of 
  little 
  else 
  than 
  a 
  white 
  silicious 
  sand 
  ; 
  

   in 
  others, 
  the 
  admixture 
  of 
  ochreous 
  clay 
  is 
  so 
  considerable, 
  as 
  to 
  fur- 
  

   nish 
  a 
  suitable 
  material 
  for 
  the 
  manufacture 
  of 
  bricks. 
  

  

  4. 
  Beneath 
  this 
  superficial 
  layer, 
  beds 
  of 
  a 
  very 
  argillaceous 
  clay 
  

   occasionally 
  occur, 
  sometimes 
  of 
  considerable 
  depth 
  and 
  extent, 
  and 
  of 
  

   a 
  texture 
  to 
  be 
  useful 
  in 
  puddling. 
  Its 
  colour 
  is 
  various, 
  being 
  in 
  some 
  

   places 
  a 
  dark 
  blue 
  or 
  green, 
  in 
  others 
  a 
  bright 
  red 
  or 
  dingy 
  yellow. 
  

   Wherever 
  found, 
  its 
  upper 
  boundary 
  is 
  remarkably 
  even 
  and 
  horizon- 
  

   tal 
  ; 
  but 
  where 
  it 
  rests 
  upon 
  beds 
  of 
  fossil 
  shells, 
  its 
  lower 
  limit 
  con- 
  

   forms 
  to 
  all 
  the 
  irregularities 
  of 
  surface 
  which 
  those 
  beds 
  usually 
  

   present. 
  Its 
  appearance, 
  in 
  some 
  places, 
  is 
  that 
  of 
  a 
  steep, 
  almost 
  per- 
  

   pendicular 
  wall 
  of 
  smooth 
  surface, 
  and 
  divided 
  by 
  very 
  narrow 
  lines 
  

   running 
  horizontally. 
  These 
  narrow 
  lines, 
  at 
  a 
  distance 
  of 
  from 
  five 
  

   inches 
  to 
  a 
  foot 
  asunder, 
  are 
  formed 
  by 
  a 
  more 
  ferruginous 
  and 
  silicious 
  

   clay. 
  At 
  Bellefield, 
  on 
  the 
  York 
  river, 
  seven 
  miles 
  from 
  Williams- 
  

   burg, 
  this 
  deposit 
  may 
  be 
  seen 
  overlying 
  the 
  stratum 
  containing 
  shells, 
  

   in 
  some 
  places 
  having 
  a 
  thickness 
  of 
  from 
  twelve 
  to 
  fifteen 
  feet, 
  and 
  

   then 
  gradually 
  fining 
  out 
  and 
  passing 
  into 
  a 
  light 
  coloured 
  and 
  coarser 
  

   mass. 
  The 
  upper 
  surface 
  is 
  horizontal, 
  and 
  the 
  lines 
  of 
  division 
  above 
  

   alluded 
  to 
  are 
  perfectly 
  parallel 
  and 
  regular. 
  The 
  lower 
  surface 
  of 
  

   the 
  clay 
  conforms 
  to 
  that 
  of 
  the 
  shell 
  stratum 
  upon 
  which 
  it 
  rests. 
  

   In 
  many 
  places 
  these 
  argillaceous 
  beds 
  consist 
  of 
  a 
  yellowish 
  clay, 
  beau- 
  

   tifully 
  variegated 
  by 
  streaks 
  of 
  red 
  and 
  blue. 
  

  

  