﻿GEOLOGY. 
  247 
  

  

  the 
  Mississippi 
  River 
  at 
  the 
  present 
  day 
  as 
  the 
  basis 
  of 
  the 
  

   calculation, 
  requiring 
  tens 
  of 
  thousands 
  of 
  years 
  to 
  

   accomplish 
  ; 
  during 
  the 
  whole 
  of 
  which 
  extended 
  cycle, 
  

   therefore, 
  some 
  dozen 
  existing 
  species 
  of 
  helices, 
  which 
  

   we 
  find 
  distributed 
  from 
  the 
  lowest 
  to 
  the 
  uppermost 
  

   portions 
  of 
  the 
  deposit, 
  would 
  seem 
  to 
  have 
  constituted 
  

   the 
  almost 
  exclusive 
  fauna 
  of 
  the 
  earth 
  subject 
  to 
  have 
  

   been 
  drifted 
  into 
  it. 
  

  

  It 
  seems 
  more 
  reasonable 
  to 
  imagine 
  it 
  to 
  have 
  been 
  

   swept 
  from 
  the 
  surface 
  of 
  pre-existing 
  land, 
  teeming 
  at 
  

   the 
  time, 
  with 
  these 
  terrestrial 
  testacea, 
  by 
  the 
  drift 
  with 
  

   which 
  it 
  is 
  found 
  associated. 
  

  

  Having 
  no 
  rocks 
  in 
  place 
  here 
  susceptible 
  of 
  retaining 
  

   the 
  scratching 
  t)r 
  grooving 
  made 
  by 
  the 
  moving 
  block 
  in 
  

   passing 
  over 
  them, 
  as 
  in 
  the 
  more 
  Northern 
  States, 
  and 
  

   by 
  which 
  the 
  direction 
  of 
  the 
  drift 
  has 
  been 
  determined, 
  

   we 
  have 
  here 
  to 
  conjecture 
  the 
  course 
  from 
  the 
  position 
  

   of 
  the 
  possihie 
  original 
  localities 
  of 
  the 
  transported 
  detri- 
  

   tus, 
  and 
  the 
  direction 
  of 
  the 
  mountain 
  ranges 
  from 
  which 
  

   tliej^ 
  are 
  supposed 
  to 
  be 
  derived. 
  

  

  In 
  reference 
  to 
  the 
  character 
  of 
  the 
  small 
  pebbles 
  and 
  

   boulders 
  of 
  the 
  deposit, 
  specimens 
  of 
  which 
  were 
  sent 
  to 
  

   Dr. 
  Locke 
  several 
  years 
  since, 
  he 
  remarked 
  that 
  they 
  

   were 
  very 
  interesting, 
  as 
  tending 
  to 
  prove 
  the 
  wide 
  dis- 
  

   persion 
  of 
  the 
  drift, 
  many 
  of 
  them 
  being 
  identified 
  with 
  

   the 
  rocks 
  found 
  in 
  place 
  by 
  Dr. 
  Owen 
  and 
  himself 
  in 
  the 
  

   survey 
  of 
  Iowa 
  and 
  Wisconsin. 
  

  

  It 
  is 
  probable, 
  however, 
  that 
  we 
  need 
  not 
  look 
  so 
  far 
  

   for 
  the 
  primitive 
  beds 
  of 
  these 
  rocks 
  if 
  we 
  suppose 
  them 
  

   to 
  have 
  pursued 
  the 
  usual 
  course 
  of 
  diluvial 
  currents, 
  

   that 
  is, 
  a 
  southeasterly 
  direction. 
  We 
  may, 
  perhaps, 
  

   find 
  their 
  origin 
  in 
  those 
  insulated 
  mountain 
  ranges, 
  the 
  

   Ozark 
  Mountains 
  and 
  the 
  Washita 
  Hills 
  in 
  Arkansas 
  

   and 
  Missouri, 
  distant 
  two 
  and 
  three 
  hundred 
  miles 
  only 
  

  

  