﻿172 
  Geological 
  Survey 
  of 
  Louisiana 
  ' 
  [Sect. 
  

  

  the 
  raft. 
  He 
  says 
  : 
  " 
  Having 
  recovered 
  some 
  of 
  the 
  benches 
  of 
  

   Maj. 
  Howell's 
  and 
  Lieut. 
  Woodruff's 
  surveys, 
  and 
  reduced 
  the 
  

   levels 
  to 
  Cairo 
  datum, 
  it 
  is 
  found 
  that 
  the 
  water 
  line 
  has 
  fallen 
  

   more 
  than 
  15 
  feet 
  at 
  the 
  head 
  of 
  the 
  raft, 
  diminishing 
  to 
  about 
  

   3 
  feet, 
  at 
  Shreveport, 
  while 
  a 
  similar 
  reduction 
  has 
  been 
  going 
  

   on 
  in 
  the 
  river 
  below."* 
  Thus 
  the 
  river 
  is 
  tending 
  to 
  return 
  to 
  

   the 
  conditions 
  which 
  existed 
  before 
  the 
  raft 
  period. 
  

  

  Drainage 
  of 
  the 
  lakes. 
  — 
  In 
  the 
  lake 
  region 
  the 
  irregular 
  deposi- 
  

   tion 
  of 
  sediment 
  has 
  rendered 
  the 
  return 
  of 
  that 
  region 
  to 
  pre- 
  

   raft 
  slower 
  than 
  in 
  the 
  main 
  channel. 
  Certain 
  of 
  the 
  old 
  

   channels 
  have 
  been 
  more 
  than 
  filled 
  with 
  sediment 
  and 
  the 
  

   streams 
  which 
  have 
  been 
  forced 
  by 
  this 
  filling 
  to 
  flow 
  over 
  older, 
  

   harder 
  beds 
  have 
  not 
  yet 
  succeeded 
  in 
  cutting 
  channels 
  in 
  them 
  

   to 
  a 
  depth 
  equal 
  to 
  the 
  depth 
  of 
  the 
  old 
  channels. 
  The 
  reduc- 
  

   tion 
  in 
  the 
  size 
  of 
  the 
  lakes, 
  though 
  hindered 
  in 
  this 
  way, 
  has 
  

   nevertheless 
  been 
  very 
  marked. 
  Sodo 
  lake 
  is 
  a 
  very 
  noticeable 
  

   instance 
  of 
  this 
  reduction 
  in 
  size. 
  (Compare 
  plates 
  14 
  and 
  16.) 
  

  

  Poston's 
  lake 
  has 
  returned 
  to 
  very 
  nearly 
  it 
  former 
  condition. 
  

   This 
  is 
  because 
  the 
  raft 
  had 
  not 
  been 
  above 
  the 
  mouth 
  of 
  Pos- 
  

   ton's 
  bayou 
  long 
  enough 
  to 
  fill 
  its 
  old 
  channel, 
  and 
  hence 
  this 
  

   lake 
  experienced 
  none 
  of 
  the 
  difficulties 
  of 
  the 
  lower 
  lakes. 
  

  

  At 
  Silver 
  Lakef 
  the 
  former 
  outlet 
  has 
  been 
  entirely 
  filled 
  and 
  

   the 
  water 
  is 
  engaged 
  in 
  cutting 
  a 
  new 
  channel 
  through 
  the 
  older 
  

   clays 
  on 
  which 
  it 
  has 
  been 
  forced. 
  

  

  Simpson's 
  lake, 
  a 
  lake 
  which 
  formerly 
  existed 
  just 
  above 
  

   Elmer's 
  baj'ou, 
  and 
  Dooley's 
  lake, 
  have 
  been 
  almost 
  entirely 
  

   obliterated. 
  During 
  the 
  raft 
  period 
  they 
  were 
  almost 
  completely 
  

   filled 
  with 
  sediment 
  and 
  after 
  the 
  removal 
  of 
  the 
  raft 
  the 
  lower- 
  

   ing 
  of 
  the 
  river 
  channel 
  by 
  erosion 
  completed 
  the 
  drainage. 
  

  

  The 
  cutting 
  out 
  of 
  the 
  river 
  channel 
  has 
  resulted 
  also 
  in 
  the 
  

   partial 
  drainage 
  of 
  the 
  small 
  lakes 
  in 
  the 
  bends 
  on 
  the 
  east 
  side 
  

   of 
  the 
  river. 
  Marks' 
  lake 
  has 
  shrunk 
  to 
  two 
  small 
  lakes, 
  and 
  

   the 
  encroachment 
  of 
  the 
  river 
  on 
  Adger's 
  lake 
  threatens 
  to 
  com- 
  

   pletely 
  destroy 
  it. 
  Dutch 
  John's 
  lake 
  has 
  shrunk 
  to 
  about 
  one- 
  

  

  *An. 
  Rept. 
  Chief 
  of 
  Eng. 
  for 
  1S93, 
  pp. 
  1909-1910, 
  1893. 
  

  

  f 
  This 
  Silver 
  Lake 
  which 
  occupied 
  a 
  valley 
  in 
  Coushatta 
  bluffs, 
  should 
  not 
  

   be 
  confused 
  with 
  the 
  now 
  dry 
  Silver 
  lake 
  near 
  Shreveport, 
  which 
  has 
  entirely 
  

   drained 
  since 
  the 
  removal 
  of 
  the 
  raft. 
  

  

  