﻿112 
  Geological 
  Survey 
  of 
  Louisiana 
  [Sect. 
  

  

  was 
  named 
  from 
  Port 
  Hudson, 
  Louisiana, 
  where 
  the 
  typical 
  

   exposure 
  is 
  found. 
  

  

  General 
  characteristics. 
  — 
  This 
  formation 
  consists 
  of 
  beds 
  of 
  

   dark 
  colored 
  clays, 
  commonly 
  blue, 
  black 
  or 
  green 
  but 
  some- 
  

   times 
  gray 
  and 
  yellow, 
  containing 
  calcareous 
  concretions 
  and 
  

   occasional 
  beds 
  of 
  gray 
  sand 
  and 
  slit. 
  The 
  blue 
  clay 
  which 
  is 
  

   probably 
  the 
  most 
  distinctive 
  bed 
  commonly 
  contains 
  stumps 
  and 
  

   trunks 
  of 
  cypress 
  and 
  other 
  lowland 
  trees. 
  

  

  It 
  shows 
  two 
  very 
  distinct 
  facies 
  : 
  a 
  marine 
  and 
  fresh 
  water. 
  

   Along 
  the 
  gulf 
  coast 
  the 
  littoral 
  portion 
  of 
  the 
  formation 
  com- 
  

   monly 
  contains 
  marine 
  and, 
  near 
  the 
  old 
  coast 
  line, 
  brackish 
  water 
  

   shells. 
  The 
  river 
  portions 
  contain 
  cypress 
  stumps, 
  driftwood 
  

   and 
  occasional 
  fresh 
  water 
  shells. 
  

  

  Synonymy. 
  — 
  This 
  development 
  of 
  marine 
  facies 
  has 
  given 
  rise 
  

   to 
  two 
  very 
  different 
  meanings 
  for 
  the 
  term 
  Port 
  Hudson. 
  In 
  

   the 
  river 
  where 
  the 
  Port 
  Hudson 
  is 
  strongly 
  differentiated 
  by 
  

   physical 
  characters 
  from 
  the 
  loess 
  and 
  yellow 
  loam 
  and 
  separated 
  

   from 
  the 
  very 
  similar 
  recent 
  deposits 
  by 
  an 
  erosion 
  interval, 
  the 
  

   term 
  Port 
  Hudson 
  is 
  restricted 
  to 
  a 
  fairly 
  limited 
  group 
  of 
  clays 
  

   at 
  the 
  base 
  of 
  the 
  Quaternary 
  series. 
  On 
  the 
  coast 
  where 
  depo- 
  

   sition 
  has 
  been 
  going 
  on 
  continuously 
  and 
  where 
  the 
  deposits 
  of 
  

   to-day 
  are 
  forming 
  under 
  the 
  same 
  conditions 
  and 
  contain 
  the 
  

   same 
  marine 
  forms 
  as 
  the 
  earlier 
  Quaternary 
  beds, 
  it 
  is 
  impossible 
  

   to 
  distinguish 
  between 
  them. 
  This 
  has 
  led 
  Hilgard 
  to 
  uncon- 
  

   sciously 
  use 
  the 
  term 
  Port 
  Hudson 
  in 
  the 
  costal 
  region 
  to 
  cover 
  

   everything 
  except 
  the 
  recent 
  sea 
  marsh 
  deposits. 
  That 
  is, 
  in 
  the 
  

   the 
  costal 
  region 
  the 
  Port 
  Hudson 
  not 
  only 
  includes 
  the 
  equiv- 
  

   alents 
  of 
  the 
  Port 
  Hudson 
  of 
  the 
  valley 
  but 
  the 
  marine 
  equiv- 
  

   alents 
  of 
  the 
  loess, 
  the 
  yellow 
  loam 
  and 
  in 
  all 
  probability 
  a 
  part 
  

   of 
  the 
  alluvium. 
  

  

  The 
  Port 
  Hudson 
  bluff, 
  which 
  is 
  the 
  typical 
  exposure 
  for 
  the 
  

   formation, 
  represents 
  only 
  the 
  fluviatile 
  development. 
  This 
  led 
  

   Johnson 
  in 
  1890* 
  to 
  propose 
  the 
  name 
  Pontchartrain 
  clays 
  for 
  

   for 
  the 
  marine 
  equivalents 
  of 
  the 
  Port 
  Hudson. 
  The 
  Pontchar- 
  

   trian 
  clays 
  consist 
  of 
  brownish 
  or 
  yellowish 
  blue 
  clay 
  with 
  sand 
  

   partings, 
  and 
  contains 
  a 
  few 
  stumps 
  and 
  marine 
  shells. 
  At 
  the 
  

  

  * 
  Bull. 
  Geol, 
  Soc. 
  Am., 
  vol. 
  2, 
  pp. 
  20-25, 
  and 
  Am. 
  Jour, 
  Sci., 
  vol. 
  40, 
  pp. 
  

   332-333. 
  1890. 
  

  

  