﻿Galloway 
  — 
  Rounding 
  of 
  Sand 
  by 
  Solution. 
  275 
  

  

  tion 
  and 
  abrasion. 
  The 
  smallest 
  perfectly 
  round 
  grain 
  

   of 
  quartz 
  in 
  this 
  sand 
  was 
  -06 
  mm. 
  in 
  diameter. 
  

  

  When 
  grains 
  of 
  calcite 
  have 
  been 
  rounded 
  by 
  solution 
  

   in 
  warm 
  acid 
  and 
  which 
  have 
  brilliant, 
  smooth 
  surfaces, 
  

   are 
  subjected 
  to 
  solution 
  in 
  a 
  very 
  weak, 
  cold 
  acid, 
  the 
  

   surfaces 
  are 
  etched 
  and 
  become 
  dull 
  in 
  appearance, 
  show- 
  

   ing 
  that 
  the 
  rate 
  of 
  solution 
  has 
  more 
  effect 
  on 
  the 
  char- 
  

   acter 
  of 
  the 
  surfaces 
  produced 
  than 
  on 
  the 
  shape 
  of 
  grain 
  

   produced 
  by 
  solution. 
  

  

  Time. 
  — 
  All 
  minerals 
  are 
  soluble 
  in 
  water 
  if 
  sufficient 
  

   time 
  is 
  given, 
  and 
  especially 
  if 
  alkalis 
  or 
  acids 
  are 
  present 
  

   in 
  the 
  water. 
  Quartz 
  can 
  be 
  dissolved 
  in 
  a 
  few 
  hours 
  in 
  

   hot 
  water 
  under 
  pressure. 
  The 
  temperature 
  and 
  pres- 
  

   sure 
  of 
  water 
  in 
  which 
  sands 
  are 
  accumulated, 
  however, 
  

   are 
  not 
  high 
  enough 
  to 
  be 
  important 
  factors 
  in 
  solution. 
  

   Just 
  how 
  rapidly 
  solution 
  takes 
  place 
  in 
  nature 
  is 
  not 
  

   known, 
  but 
  it 
  probably 
  requires 
  hundreds, 
  perhaps 
  thou- 
  

   sands, 
  of 
  years 
  to 
  produce 
  any 
  noticeable 
  effect 
  on 
  the 
  

   roundness 
  of 
  a 
  grain 
  of 
  sand. 
  

  

  When 
  the 
  surface 
  exposed 
  remains 
  constant, 
  and 
  the 
  

   solute 
  far 
  from 
  the 
  saturation 
  point, 
  the 
  rate 
  of 
  solution 
  

   varies 
  directly 
  with 
  the 
  time. 
  When 
  other 
  factors 
  remain 
  

   constant, 
  the 
  longer 
  solution 
  acts 
  the 
  more 
  nearly 
  round 
  

   the 
  grains 
  become. 
  

  

  The 
  brilliant, 
  glistening 
  surface 
  of 
  the 
  grains 
  of 
  most 
  

   beach 
  sands 
  is 
  no 
  doubt 
  partly 
  due 
  to 
  solution. 
  The 
  sur- 
  

   faces 
  of 
  quartz 
  grains 
  which 
  I 
  mechanically 
  rounded 
  in 
  

   water 
  were 
  pearly, 
  not 
  glassy 
  like 
  freshly 
  broken 
  quartz, 
  

   nor 
  "frosted" 
  as 
  in 
  old, 
  wind-worn 
  sands, 
  nor 
  like 
  old 
  

   beach 
  sands 
  like 
  that 
  noted 
  by, 
  Merrill 
  from 
  Santa 
  Kosa 
  

   Island, 
  Florida, 
  5 
  whose 
  history 
  seems 
  to 
  be 
  complex. 
  

  

  Size 
  of 
  grains. 
  — 
  The 
  smaller 
  the 
  grains 
  the 
  more 
  

   rapidly 
  and 
  the 
  more 
  completely 
  they 
  are 
  rounded 
  by 
  

   solution. 
  Grains 
  of 
  sodium 
  chloride 
  and 
  of 
  calcite 
  -2 
  or 
  

   •3 
  mm. 
  in 
  diameter 
  partially 
  dissolved 
  experimentally 
  are 
  

   subround 
  and 
  retain 
  some 
  of 
  their 
  original 
  form, 
  while 
  

   grains 
  of 
  the 
  same 
  materials 
  under 
  otherwise 
  identical 
  

   conditions 
  but 
  less 
  than 
  -1 
  mm. 
  in 
  diameter 
  were 
  mostly 
  

   subspherical. 
  Fig. 
  4 
  shows 
  the 
  forms 
  assumed 
  by 
  com- 
  

   mon 
  table 
  salt 
  undergoing 
  solution 
  in 
  water. 
  

  

  The 
  rate 
  of 
  solution 
  varies 
  with 
  the 
  area 
  of 
  surface 
  

   acted 
  upon, 
  hence 
  finely 
  divided 
  substances 
  dissolve 
  more 
  

   rapidly 
  than 
  the 
  same 
  quantity 
  in 
  larger 
  pieces. 
  The 
  

  

  5 
  Merrill, 
  Rocks, 
  Rock 
  Weathering 
  and 
  Soils, 
  p. 
  243, 
  1904. 
  

  

  