﻿GEOLOGY. 
  251 
  

  

  Blocks 
  of 
  chert, 
  of 
  cubical 
  or 
  angular 
  forms, 
  which 
  

   have 
  either 
  not 
  been 
  rolled, 
  or 
  have, 
  since 
  their 
  deposit 
  

   tion, 
  been 
  broken 
  into 
  these 
  forms 
  by 
  their 
  natural 
  lines 
  

   of 
  fracture, 
  are 
  occasionally 
  found 
  measuring 
  two 
  cubic 
  

   feet 
  or 
  more; 
  and 
  a 
  block 
  of 
  pure 
  milk 
  quartz 
  weighing 
  

   about 
  ten 
  pounds 
  has 
  been 
  obtained. 
  

  

  The 
  largest 
  boulder 
  seen, 
  was 
  found 
  six 
  or 
  seven 
  miles 
  

   north 
  of 
  Vicksburg, 
  near 
  the 
  base 
  of 
  the 
  range 
  of 
  bluffs 
  

   known 
  as 
  the 
  Walnut 
  Hills. 
  It 
  is 
  of 
  a 
  symmetrical, 
  

   ovate 
  form, 
  very 
  similar 
  in 
  shape 
  to 
  the 
  ferruginous 
  

   quartz 
  pebbles 
  before 
  spoken 
  of, 
  and 
  approaching 
  them 
  

   somewhat 
  in 
  mineral 
  composition, 
  and 
  of 
  somewhat 
  

   greater 
  convexity 
  of 
  form. 
  It 
  measures 
  about 
  three 
  feet 
  

   in 
  length 
  by 
  more 
  than 
  two 
  in 
  its 
  greatest 
  transverse 
  

   diameter; 
  the 
  weight 
  being 
  conjectured 
  to 
  be 
  at 
  least 
  

   five 
  hundred 
  pounds. 
  

  

  Another 
  angular 
  block 
  of 
  perhaps 
  equal 
  dimensions 
  

   has 
  been 
  seen 
  in 
  another 
  locality. 
  

  

  The 
  general 
  limits 
  of 
  distribution 
  of 
  this 
  drift 
  have 
  

   before 
  been 
  stated. 
  The 
  heaviest 
  deposits 
  that 
  have 
  

   come 
  under 
  my 
  observation, 
  both 
  as 
  to 
  the 
  extent 
  of 
  the 
  

   beds 
  and 
  dimensions 
  of 
  the 
  boulders, 
  are 
  those 
  on 
  Big 
  

   Sand 
  in 
  Claiborne 
  County, 
  some 
  twenty 
  miles 
  northeast- 
  

   wardly 
  from 
  Port 
  Gibson. 
  This 
  is 
  exposed 
  for 
  several 
  

   miles 
  along 
  the 
  widely 
  cut 
  bed 
  of 
  the 
  creek, 
  and 
  in 
  

   several 
  others 
  in 
  the 
  vicinity, 
  extending 
  to 
  and 
  along 
  

   the 
  Bayou 
  Pierre. 
  

  

  Others, 
  not 
  much 
  less 
  considerable, 
  are 
  found 
  on 
  St. 
  

   Catherine's 
  Creek, 
  near 
  Washington, 
  and 
  on 
  some 
  of 
  the 
  

   small 
  branches 
  of 
  Cole's 
  Creek, 
  in 
  Adams 
  and 
  Jefferson 
  

   Counties. 
  

  

  An 
  extensive 
  gravel 
  bar, 
  extending 
  over 
  a 
  surface 
  

   of 
  more 
  than 
  three 
  hundred 
  acres, 
  is 
  seen 
  at 
  Diamond 
  

   Island, 
  in 
  the 
  Mississippi, 
  fifteen 
  miles 
  below 
  Vicksburg. 
  

  

  