﻿270 
  Galloivay 
  — 
  Rounding 
  of 
  Sand 
  by 
  Solution. 
  

  

  Akt. 
  XVI. 
  — 
  The 
  Rounding 
  of 
  Grains 
  of 
  Sand 
  by 
  Solution; 
  

   by 
  J. 
  J. 
  Galloway. 
  

  

  Introduction 
  

  

  The 
  degree 
  of 
  roundness 
  of 
  grains 
  of 
  sand 
  is 
  con- 
  

   sidered 
  by 
  many 
  geologists 
  as 
  of 
  prime 
  importance 
  in 
  the 
  

   interpretation 
  of 
  the 
  conditions 
  of 
  deposition 
  of 
  sand- 
  

   stones. 
  A 
  "millet 
  seed/' 
  quartz 
  sandstone, 
  that 
  is, 
  one 
  

   consisting 
  wholly 
  of 
  well 
  rounded 
  grains, 
  is 
  regarded 
  as 
  

   indicating 
  eolation 
  and 
  the 
  deposition 
  of 
  the 
  sand 
  under 
  

   desert 
  conditions. 
  

  

  Special 
  importance 
  has 
  been 
  attached 
  to 
  the 
  presence 
  

   of 
  well 
  rounded 
  grains 
  below 
  one-tenth 
  millimeter 
  in 
  

   diameter 
  as 
  indicating 
  that 
  such 
  grains 
  were 
  rounded 
  by 
  

   abrasion 
  in 
  the 
  wind, 
  and 
  could 
  not 
  be 
  rounded 
  in 
  water. 
  1 
  

   This 
  idea 
  evidently 
  originated 
  in 
  Daubree's 
  statement, 
  

   ' 
  i 
  The 
  dimensions 
  of 
  grains 
  which 
  can 
  float 
  in 
  very 
  feebly 
  

   agitated 
  water 
  appear 
  to 
  be 
  about 
  one-tenth 
  millimeter 
  

   in 
  average 
  diameter. 
  All 
  finer 
  sand 
  will 
  be 
  without 
  

   doubt 
  angular." 
  2 
  

  

  I 
  have 
  proved 
  by 
  experiment 
  that 
  grains 
  of 
  calcite, 
  

   dolomite, 
  mica 
  and 
  hornblende, 
  ranging 
  in 
  size 
  all 
  the 
  

   way 
  down 
  to 
  -01 
  mm. 
  in 
  diameter 
  can 
  be 
  rounded 
  by 
  

   mutual 
  abrasion 
  in 
  water 
  in 
  fifty 
  hours 
  at 
  a 
  velocity 
  of 
  

   four 
  miles 
  an 
  hour; 
  that 
  the 
  lower 
  effective 
  limit 
  of 
  

   rounding 
  by 
  abrasion 
  in 
  water 
  is 
  about 
  -05 
  mm. 
  ; 
  and 
  that 
  

   the 
  rate 
  of 
  rounding 
  becomes 
  progressively 
  slower 
  after 
  

   the 
  grains 
  are 
  reduced 
  to 
  a 
  diameter 
  of 
  about 
  -2 
  mm., 
  

   below 
  which 
  size 
  the 
  time 
  taken 
  to 
  round 
  grains 
  is 
  greatly 
  

   lengthened. 
  I 
  believe 
  these 
  results 
  would 
  apply 
  to 
  quartz 
  

   grains 
  if 
  the 
  time 
  were 
  sufficiently 
  lengthened, 
  that 
  is 
  to 
  

   at 
  least 
  800 
  hours 
  at 
  four 
  miles 
  an 
  hour. 
  The 
  smallest 
  

   spherical 
  grain 
  of 
  quartz 
  I 
  was 
  able 
  to 
  produce 
  in 
  150 
  

   hours 
  at 
  four 
  miles 
  an 
  hour 
  measured 
  -2 
  mm. 
  in 
  diameter. 
  

  

  The 
  fact, 
  however, 
  that 
  fragments 
  of 
  minerals 
  are 
  

   rounded 
  by 
  solution, 
  and 
  that 
  this 
  process 
  may 
  be 
  of 
  cor- 
  

   responding 
  geological 
  importance, 
  seems 
  to 
  have 
  escaped 
  

   the 
  attention 
  of 
  most 
  students 
  of 
  sands. 
  Sorby, 
  almost 
  

   the 
  first 
  and 
  one 
  of 
  the 
  closest 
  observers 
  of 
  the 
  character- 
  

   istics 
  of 
  sands, 
  recognized 
  the 
  factor 
  of 
  corrosion 
  in 
  the 
  

   production 
  of 
  rounded 
  grains 
  of 
  quartz. 
  He 
  says, 
  3 
  

  

  l 
  Grabau, 
  Principles 
  of 
  Stratigraphy, 
  pp. 
  226, 
  25.°,, 
  553, 
  3913. 
  

  

  2 
  Literal 
  translation 
  from 
  Daubree, 
  Geologie 
  Experimental, 
  p. 
  256, 
  1879. 
  

  

  3 
  Quart. 
  Jour. 
  Geol. 
  Soc. 
  London, 
  vol. 
  36, 
  Proceedings, 
  p. 
  47, 
  1880. 
  

  

  