﻿'Kindle 
  — 
  Factor 
  in 
  Rounding 
  of 
  Sand 
  Grains. 
  131 
  

  

  Aet. 
  XXIX. 
  — 
  A 
  Neglected 
  Factor 
  in 
  the 
  Rounding 
  of 
  

   Sand 
  Grains;* 
  by 
  E. 
  M. 
  Kixdle. 
  

  

  Since 
  rounding, 
  or 
  subspherical 
  shape, 
  in 
  sand 
  grains 
  

   has 
  come 
  to 
  be 
  regarded 
  as 
  one 
  of 
  the 
  criteria 
  of 
  dune 
  

   sand 
  deposits, 
  the 
  desirability 
  of 
  knowing 
  all 
  of 
  the 
  fac- 
  

   tors 
  which 
  contribute 
  to 
  the 
  rounding 
  of 
  sand 
  grains 
  has 
  

   become 
  increasingly 
  important. 
  It 
  is 
  generally 
  assumed 
  

   that 
  the 
  higher 
  degree 
  of 
  rounding 
  which 
  characterizes 
  

   dune 
  sands 
  as 
  compared 
  with 
  sea 
  sands 
  is 
  the 
  result 
  of 
  

   wind 
  action. 
  

  

  The 
  theory 
  of 
  the 
  greater 
  potency 
  of 
  wind 
  action 
  in 
  

   rounding 
  sand 
  grains 
  was 
  clearly 
  stated 
  by 
  Mackie 
  in 
  the 
  

   following 
  passage: 
  "This 
  leads 
  us 
  to 
  investigate 
  why 
  

   wind 
  should 
  be 
  a 
  more 
  potent 
  agent 
  in 
  the 
  rounding 
  pro- 
  

   cess 
  than 
  water. 
  In 
  air 
  the 
  particles 
  roll 
  with 
  their 
  full 
  

   weight. 
  In 
  water 
  they 
  lose 
  weight, 
  by 
  the 
  weight 
  an 
  

   equal 
  volume 
  of 
  water, 
  so 
  that 
  in 
  water 
  they 
  roll 
  with 
  only 
  

   a 
  fraction 
  of 
  their 
  weight. 
  This 
  is 
  one 
  reason 
  why 
  much 
  

   larger 
  particles 
  are 
  moved 
  by 
  water 
  than 
  by 
  wind. 
  It 
  

   should 
  be 
  remembered 
  however 
  that 
  in 
  the 
  rounding 
  of 
  

   the 
  larger 
  particles 
  or 
  pebbles 
  it 
  is 
  only 
  the 
  exceptional 
  

   force 
  of 
  the 
  current 
  that 
  is 
  concerned 
  whereas 
  in 
  the 
  case 
  

   of 
  wind, 
  a 
  relatively 
  large 
  proportion 
  of 
  the 
  work 
  of 
  

   rounding 
  is 
  probablv 
  done 
  by 
  comparatively 
  low 
  veloci- 
  

   ties." 
  1 
  

  

  Sowerby 
  pointed 
  out 
  the 
  rapidly 
  decreasing 
  power 
  of 
  

   water 
  to 
  produce 
  wear 
  on 
  the 
  surface 
  of 
  a 
  sand 
  grain 
  with 
  

   reduction 
  of 
  diameter. 
  "Perhaps, 
  then 
  we 
  may 
  conclude 
  

   that 
  a 
  o-rain 
  1/10 
  of 
  an 
  inch 
  in 
  diameter 
  would 
  be 
  worn 
  

   as 
  much 
  or 
  more 
  in 
  drifting 
  a 
  mile 
  as 
  a 
  grain 
  1/1000 
  of 
  

   an 
  inch 
  in 
  being 
  drifted 
  100 
  miles. 
  ' 
  ' 
  2 
  

  

  Daubree 
  3 
  argued 
  that 
  a 
  minimum 
  size 
  is 
  reached 
  in 
  the 
  

   reduction 
  of 
  sand 
  grains 
  by 
  water 
  below 
  which 
  no 
  reduc- 
  

   tion 
  can 
  occur 
  since 
  quartz 
  grains 
  less 
  than 
  0-1 
  mm. 
  will 
  

   float 
  in 
  water 
  very 
  slightly 
  agitated. 
  Because 
  of 
  the 
  

   cushion 
  of 
  water 
  which 
  keeps 
  extremely 
  small 
  particles 
  

   from 
  contact 
  with 
  each 
  other 
  he 
  concluded 
  that 
  ' 
  ' 
  any 
  finer 
  

   grained 
  sand 
  would 
  doubtless 
  be 
  angular." 
  In 
  the 
  

  

  * 
  Published 
  with 
  the 
  permission 
  of 
  the 
  Director 
  of 
  the 
  Geological 
  Survey 
  

   of 
  Canada. 
  

  

  1 
  Mackie, 
  Wm. 
  : 
  Laws 
  that 
  Govern 
  Rounding 
  of 
  Particles 
  of 
  Sand, 
  Edin- 
  

   burgh 
  Geol. 
  Society, 
  vol. 
  7, 
  pp. 
  309-310, 
  1893-98. 
  

  

  - 
  Sowerby, 
  Anniversary 
  Address, 
  Quart. 
  Jour. 
  Geol. 
  Soc, 
  p. 
  59, 
  18S0. 
  

  

  3 
  £tudes 
  synthetiques 
  de 
  Geologic 
  erperimentale, 
  p. 
  256, 
  1S79. 
  

  

  