﻿ii8 
  Geoi^ogical 
  Survey 
  of 
  L,ouisiana 
  [Sect. 
  

  

  owe 
  their 
  death 
  and 
  present 
  position 
  to 
  a 
  sinking 
  of 
  the 
  land.* 
  

   As 
  a 
  subsidence 
  is 
  now 
  progressing 
  in 
  this 
  region 
  the 
  relation 
  

   between 
  the 
  partly 
  live 
  and 
  partly 
  dead 
  cypress 
  trees 
  and 
  the 
  

   prostrate 
  trunks 
  and 
  stumps 
  in 
  the 
  adjacent 
  marsh 
  seems 
  very 
  

   clear. 
  

  

  The 
  Alluvium. 
  — 
  In 
  the 
  valley, 
  where 
  a 
  period 
  of 
  erosion 
  has 
  

   separated 
  the 
  old 
  alluvium 
  from 
  the 
  new, 
  there 
  is 
  some 
  hope 
  of 
  

   distinguishing 
  between 
  the 
  two. 
  But 
  even 
  here 
  we 
  are 
  con- 
  

   fronted 
  by 
  the 
  fact 
  that 
  the 
  local 
  cypress 
  swamp 
  deposits 
  of 
  

   to-day 
  and 
  the 
  cypress 
  swamp 
  deposits 
  of 
  the 
  Port 
  Hudson 
  

   period 
  must 
  be 
  very 
  similar. 
  As 
  a 
  result 
  of 
  work 
  in 
  the 
  Yazoo 
  

   bottoms, 
  Dr. 
  E. 
  A. 
  Smith 
  came 
  to 
  the 
  conclusion 
  that 
  the 
  Port 
  

   Hudson 
  blue 
  clay 
  was 
  characterized 
  by 
  calcareous 
  concretions 
  

   which 
  are 
  entirely 
  lacking 
  in 
  the 
  recent 
  deposits. 
  

  

  The 
  thickness 
  of 
  the 
  material 
  which 
  may 
  be 
  unquestionably 
  

   attributed 
  to 
  the 
  deposits 
  of 
  the 
  river 
  during 
  the 
  present 
  subsi- 
  

   dence 
  is 
  very 
  slight. 
  In 
  the 
  Mississippi 
  valley 
  a 
  deposit 
  of 
  over 
  

   20 
  feet 
  of 
  unquestionably 
  recent 
  river 
  formation 
  will 
  rarely 
  be 
  

   seen, 
  while 
  a 
  deposit 
  of 
  a 
  few 
  feet 
  is 
  most 
  common. 
  f 
  The 
  same 
  

   thing 
  holds 
  true 
  in 
  the 
  Red 
  river 
  valley. 
  

  

  Quaternary 
  Phenomena 
  Other 
  Than 
  Deposition 
  and 
  

  

  Erosion 
  

  

  LocAi, 
  Crustai, 
  Movements 
  

  

  The 
  Five 
  Islands.— 
  ■'^'\xq. 
  great 
  deposits 
  of 
  sediment 
  along 
  this 
  

   coast 
  in 
  Quaternary 
  time 
  have 
  doubtless 
  greatly 
  aided 
  other 
  

   forces 
  in 
  distributing 
  the 
  equilibrium 
  of 
  the 
  crust 
  in 
  this 
  region. 
  

   After 
  the 
  deposition 
  of 
  the 
  Lafayette 
  gravel 
  and 
  some 
  of 
  the 
  

   basal 
  Quaternary 
  layers 
  and 
  before 
  the 
  deposition 
  of 
  the 
  yellow 
  

   loam 
  a 
  series 
  of 
  ver}^ 
  peculiar 
  dome-shaped 
  folds 
  and, 
  to 
  all 
  

   appearances, 
  a 
  large 
  fault 
  were 
  either 
  formed 
  or 
  assumed 
  their 
  

   present 
  position 
  along 
  the 
  southern 
  coast 
  of 
  Louisiana. 
  These 
  

   gave 
  rise 
  to 
  those 
  peculiar 
  elevations 
  along 
  the 
  coast 
  known 
  as 
  

   the 
  Five 
  Islands. 
  On 
  two 
  of 
  these 
  mammillae-like 
  protuberances, 
  

   whose 
  surfaces 
  have 
  been 
  greatly 
  ridged 
  by 
  erosion, 
  enough 
  

   borings 
  have 
  been 
  made 
  to 
  reveal 
  the 
  fact 
  that 
  the 
  underlying 
  

  

  * 
  Geologic 
  Pratique, 
  i860, 
  pp. 
  82-83. 
  

  

  f 
  Hilgard, 
  — 
  48 
  Cong, 
  rst 
  Sess., 
  House 
  Ex. 
  Doc, 
  vol.19, 
  1884, 
  pp. 
  480-481. 
  

  

  