﻿20 
  • 
  Geological 
  Survey 
  of 
  IvOuisiana 
  [Sect. 
  

  

  In 
  volume 
  2 
  of 
  his 
  Second 
  Visit 
  to 
  the 
  United 
  States, 
  pub- 
  

   lished 
  (3d 
  ed.) 
  1855, 
  Lyell 
  (p. 
  153) 
  is 
  greatly 
  impressed 
  with 
  

   the 
  stabilit}^ 
  of 
  the 
  general 
  features 
  of 
  the 
  mouths 
  of 
  the 
  Missis- 
  

   sippi, 
  and 
  concludes 
  that 
  "we 
  must 
  allow 
  an 
  enormous 
  period 
  of 
  

   time" 
  for 
  the 
  accumulation 
  of 
  the 
  material 
  constituting 
  the 
  whole 
  

   delta. 
  On 
  p. 
  250 
  he 
  estimates 
  67,000 
  years 
  for 
  the 
  time 
  required 
  

   for 
  the 
  formation 
  of 
  the 
  delta. 
  

  

  On 
  pages 
  180-182 
  he 
  describes 
  the 
  interesting 
  bluff 
  at 
  Port 
  

   Hudson 
  after 
  quoting 
  largely 
  from 
  Bartram 
  and 
  Carpenter. 
  

  

  Natchez 
  bluff 
  is 
  next 
  described 
  (p. 
  194) 
  as 
  follows 
  : 
  "The 
  lower 
  

   strata, 
  laid 
  open 
  to 
  view, 
  consist 
  of 
  gravel 
  and 
  sand, 
  destitute 
  of 
  

   organic 
  remains, 
  except 
  some 
  wood 
  and 
  silicified 
  corals, 
  and 
  other 
  

   fossils, 
  which 
  have 
  been 
  derived 
  from 
  older 
  rocks 
  ; 
  while 
  the 
  

   upper 
  sixty 
  feet 
  are 
  composed 
  of 
  yellow 
  loam, 
  presenting 
  as 
  it 
  

   wastes 
  away, 
  a 
  vertical 
  face 
  towards 
  the 
  river. 
  From 
  the 
  surface 
  

   of 
  the 
  clayey 
  precipice 
  are 
  seen 
  projecting 
  in 
  relief, 
  the 
  whitened 
  

   and 
  perfect 
  shells 
  of 
  land 
  snails 
  of 
  the 
  genera 
  Helix, 
  Heli- 
  

   ci7ia, 
  Pupa, 
  Cyclostoma, 
  Achatina 
  and 
  Sticcinea. 
  These 
  shells 
  of 
  

   which 
  we 
  collected 
  twenty 
  species, 
  are 
  all 
  specifically 
  identical 
  

   with 
  those 
  now 
  inhabiting 
  the 
  valley 
  of 
  the 
  Mississippi. 
  

  

  ' 
  ' 
  The 
  resemblance 
  of 
  this 
  loam 
  to 
  that 
  fluviatile 
  slit 
  of 
  the 
  val- 
  

   ley 
  of 
  the 
  Rhine, 
  between 
  Cologne 
  and 
  Basle, 
  which 
  is 
  generally 
  

   called 
  "loess" 
  and 
  "lehm" 
  in 
  Alsace, 
  is 
  most 
  perfect. 
  In 
  both 
  

   countries 
  the 
  genera 
  of 
  shells 
  are 
  the 
  same, 
  and 
  as, 
  in 
  the 
  ancient 
  

   alluvium 
  of 
  the 
  Rhine, 
  the 
  loam 
  sometimes 
  passes 
  into 
  a 
  lacus- 
  

   trine 
  deposit 
  containing 
  shells 
  of 
  the 
  genera 
  Lymncsa, 
  Planorbis, 
  

   and 
  Cyclas, 
  so 
  I 
  found 
  at 
  Washington, 
  about 
  seven 
  miles 
  inland 
  

   or 
  eastward 
  from 
  Natchez 
  a 
  similar 
  passage 
  of 
  the 
  American 
  

   loam 
  into 
  a 
  deposit 
  evidently 
  formed 
  in 
  a 
  pond 
  or 
  lake. 
  It 
  con- 
  

   sisted 
  of 
  marl 
  containing 
  shells 
  of 
  Lyimicea, 
  Planorbis, 
  Paludina, 
  

   Physa 
  and 
  Cyclas, 
  specifically 
  agreeing 
  with 
  testacea 
  now 
  inhab- 
  

   iting 
  the 
  United 
  States." 
  He 
  records 
  Mastadon, 
  Megalonyx, 
  

   horse, 
  stag, 
  etc., 
  from 
  these 
  loams. 
  

  

  Dickeso7i 
  a)id 
  Brown. 
  — 
  At 
  the 
  first 
  meeting 
  of 
  the 
  American 
  

   Association 
  for 
  the 
  Advancement 
  of 
  Science 
  held 
  at 
  Philadelphia 
  

   in 
  1848, 
  Dr. 
  Dickeson 
  read 
  a 
  joint 
  paper 
  on 
  "The 
  Sediment 
  of 
  

   the 
  Mississippi," 
  in 
  which 
  the 
  statement 
  is 
  made 
  that 
  the 
  delta 
  

   of 
  the 
  Mississippi 
  has 
  been 
  no 
  less 
  than 
  14,204 
  years 
  in 
  forming. 
  

   (See 
  p. 
  51, 
  Proc. 
  Am. 
  Assoc. 
  Adv. 
  Sci., 
  vol. 
  i.) 
  

  

  