﻿Galloway 
  — 
  Rounding 
  of 
  Sand 
  by 
  Solution. 
  279 
  

  

  solution 
  unaccompanied 
  by 
  movement 
  of 
  the 
  grains. 
  The 
  

   same 
  features 
  were 
  noted 
  in 
  quartz 
  grains 
  -1 
  to 
  -04 
  mm. 
  

   in 
  diameter 
  from 
  residual 
  clay 
  from 
  Brick 
  Haven, 
  Va., 
  

   and 
  in 
  decomposed 
  granite 
  from 
  the 
  District 
  of 
  Columbia. 
  

   In 
  so-called 
  loess 
  from 
  Muscatine, 
  la., 
  most 
  of 
  the 
  quartz 
  

   grains 
  are 
  round 
  or 
  subround, 
  especially 
  those 
  between 
  

   •05 
  and 
  -01 
  mm. 
  in 
  diameter, 
  and 
  the 
  surfaces 
  are 
  all 
  cor- 
  

   roded. 
  I 
  do 
  not 
  believe 
  that 
  such 
  small 
  grains 
  could 
  be 
  

   rounded 
  by 
  abrasion 
  in 
  either 
  air 
  or 
  water, 
  but 
  solution 
  

   would 
  account 
  for 
  the 
  form. 
  In 
  glacial 
  silt 
  from 
  Ithaca, 
  

   X. 
  Y., 
  the 
  quartz 
  grains 
  -1 
  mm. 
  and 
  less 
  in 
  diameter 
  are 
  

   only 
  slightly 
  corroded 
  and 
  all 
  are 
  noticeably 
  rounded, 
  dif- 
  

   fering, 
  strikingly 
  from 
  the 
  perfect 
  angularity 
  of 
  crushed 
  

   quartz 
  grains 
  of 
  the 
  same 
  sizes 
  with 
  which 
  I 
  compared 
  

   them. 
  In 
  fuller's 
  earth 
  from 
  Whigham, 
  Ga., 
  there 
  are 
  

   quartz 
  grains 
  -05 
  mm. 
  and 
  less 
  in 
  diameter, 
  and 
  most 
  of 
  

   them 
  are 
  smoothly 
  round, 
  the 
  surfaces 
  are 
  brilliant 
  and 
  

   show 
  no 
  corrosion, 
  and 
  they 
  certainly 
  were 
  not 
  produced 
  

   by 
  abrasion. 
  

  

  Streams, 
  beaches 
  and 
  springs 
  are 
  favorable 
  places 
  for 
  

   the 
  rounding 
  of 
  minute 
  grains 
  by 
  solution, 
  on 
  account 
  of 
  

   the 
  more 
  or 
  less 
  continual 
  motion 
  of 
  the 
  water 
  and 
  sand. 
  

   Moreover, 
  since 
  the 
  smaller 
  grains 
  are 
  more 
  often 
  and 
  

   longer 
  in 
  motion 
  than 
  the 
  larger 
  grains, 
  the 
  smaller 
  ones 
  

   would 
  have 
  the 
  best 
  chance 
  of 
  becoming 
  rounded 
  both 
  by 
  

   abrasion 
  and 
  by 
  solution. 
  It 
  is 
  possible 
  also 
  that 
  water 
  

   softens 
  the 
  surfaces 
  of 
  grains 
  and 
  makes 
  abrasion 
  more 
  

   rapid 
  and 
  polishing 
  more 
  complete 
  than 
  when 
  the 
  grains 
  

   are 
  dry. 
  

  

  Cleavage. 
  — 
  Cleavage 
  has 
  little 
  effect 
  on 
  the 
  shape 
  of 
  

   grain 
  produced 
  by 
  rapid 
  solution, 
  even 
  when 
  so 
  pro- 
  

   nounced 
  as 
  in 
  calcite 
  or 
  halite, 
  except 
  as 
  it 
  influences 
  the 
  

   shape 
  of 
  the 
  grain 
  before 
  solution 
  begins. 
  The 
  patterns 
  

   produced 
  on 
  crystals 
  by 
  etching 
  with 
  acid 
  is 
  due 
  to 
  molec- 
  

   ular 
  arrangement 
  rather 
  than 
  to 
  cleavage. 
  When 
  the 
  

   cleavage 
  planes 
  have 
  separated, 
  solution 
  and 
  disintegra- 
  

   tion 
  are 
  favored, 
  and 
  flat 
  or 
  irregular 
  forms 
  are 
  produced 
  

   as 
  well 
  as 
  round 
  grains 
  of 
  silt 
  or 
  clay 
  size. 
  Under 
  con- 
  

   tinued 
  solution 
  grains 
  become 
  almost 
  perfectly 
  round 
  just 
  

   before 
  they 
  disappear. 
  When 
  solution 
  is 
  slow, 
  cleavage 
  

   and 
  twinning 
  planes 
  are 
  attacked 
  more 
  rapidly 
  than 
  other 
  

   parts 
  of 
  the 
  crystal, 
  causing 
  disintegration 
  and 
  favoring 
  

   decomposition 
  rather 
  than 
  solution. 
  

  

  Purity 
  of 
  the 
  mineral. 
  — 
  Grains 
  consisting 
  of 
  more 
  than 
  

   one 
  chemical 
  substance, 
  such 
  as 
  impure 
  salts, 
  calcite, 
  

  

  