﻿Ill] 
  The 
  Fiv'e 
  Islands 
  : 
  Grand 
  Cote 
  235 
  

  

  entered 
  the 
  salt 
  far 
  enough 
  to 
  determine 
  the 
  direction 
  and 
  

   intensity 
  of 
  the 
  dip. 
  

  

  Origin 
  of 
  the 
  lakes. 
  — 
  ^Thomassy 
  in 
  his 
  visit 
  to 
  the 
  island 
  noticed 
  

   the 
  upland 
  lakes. 
  Sugar 
  House 
  pond 
  he 
  considered 
  the 
  ' 
  ' 
  orifice 
  

   where 
  the 
  hydrothermal 
  forces 
  made 
  their 
  principal 
  eruption 
  ;" 
  

   the 
  others 
  are 
  craters 
  of. 
  depression 
  similar 
  to 
  those 
  which 
  have 
  

   given 
  rise 
  to 
  the 
  numerous 
  little 
  lakes 
  of 
  southern 
  Louisiana.* 
  

   In 
  the 
  light 
  of 
  our 
  present 
  knowledge 
  of 
  the 
  islands 
  this 
  expla- 
  

   nation 
  can 
  hardl}^ 
  be 
  accepted, 
  for 
  the 
  phenomena 
  shown 
  here 
  

   cannot 
  be 
  confounded 
  with 
  that 
  exhibited 
  b}^ 
  the 
  mud-volcanoes 
  

   of 
  the 
  passes 
  of 
  the 
  Mississippi. 
  The 
  similarity 
  in 
  all 
  these 
  lake 
  

   basins 
  point 
  to 
  a 
  common 
  origin. 
  

  

  The 
  observed 
  facts 
  would 
  point 
  to 
  four 
  different 
  ways 
  in 
  which 
  

   the 
  lakes 
  might 
  have 
  been 
  formed 
  : 
  ( 
  i 
  ) 
  by 
  faulting 
  or 
  landslips 
  

   produced 
  by 
  orographic 
  movements, 
  (2) 
  by 
  faulting 
  or 
  landslips 
  

   produced 
  b\^ 
  the 
  removal 
  of 
  the 
  salt 
  by 
  subterranean 
  waters, 
  

   (3) 
  by 
  the 
  formation 
  of 
  sink 
  holes 
  like 
  those 
  of 
  limestone 
  regions 
  

   and 
  the 
  subsequent 
  stopping 
  of 
  the 
  basal 
  outlet, 
  (4) 
  by 
  the 
  irregu- 
  

   lar 
  falling 
  of 
  antecedent 
  drainage 
  channels 
  b}^ 
  Columbia 
  loam. 
  

  

  L,andslips 
  in 
  the 
  sands 
  and 
  clays 
  occasioned 
  by 
  the 
  folding 
  or 
  

   faulting 
  of 
  the 
  salt 
  bed, 
  even 
  with 
  the 
  aid 
  of 
  subsequent 
  erosion, 
  

   would 
  hardly 
  be 
  likely 
  to 
  produce 
  the 
  rounded 
  amphitheatre- 
  

   shaped 
  lake 
  valleys. 
  

  

  Many 
  of 
  the 
  local 
  faults, 
  anticlines 
  and 
  sink 
  holes 
  in 
  northern 
  

   New 
  York 
  have 
  been 
  formed 
  in 
  the 
  second 
  way 
  by 
  the 
  removal 
  

   of 
  the 
  soluble 
  matter 
  from 
  the 
  beds 
  of 
  the 
  Onondaga 
  salt 
  and 
  

   waterlime 
  groups 
  by 
  subterranean 
  waters 
  coming 
  from 
  a 
  distance. 
  

   It 
  is 
  possible, 
  though 
  hardly 
  probable, 
  that 
  the 
  lake 
  valleys 
  on 
  

   the 
  islands 
  have 
  been 
  formed 
  in 
  the 
  same 
  way. 
  The 
  lack 
  of 
  

   continuous 
  layers 
  of 
  impervious 
  strata 
  to 
  confine 
  and 
  conduct 
  

   the 
  underground 
  waters 
  would 
  strongly 
  oppose 
  this 
  theory. 
  

  

  The 
  third 
  necessitates 
  the 
  assumption 
  of 
  a 
  very 
  marked 
  subsi- 
  

   dence 
  in 
  the 
  region 
  in 
  ver)^ 
  recent 
  times, 
  an 
  assumption 
  which 
  

   is 
  supported 
  b}' 
  the 
  partiall}- 
  drowned 
  stream 
  channels 
  of 
  the 
  

   coastal 
  regions. 
  If 
  the 
  salt 
  mass 
  was 
  elevated 
  well 
  above 
  the 
  

   sea, 
  say 
  200 
  to 
  500 
  feet 
  above 
  its 
  present 
  level, 
  water 
  percolating 
  

   down 
  from 
  the 
  surface 
  of 
  the 
  island 
  would 
  dissolve 
  the 
  salt 
  and 
  

  

  * 
  Geologic 
  Pratique 
  de 
  la 
  Louisiana, 
  p. 
  82, 
  i860. 
  

  

  