﻿278 
  Galloway 
  — 
  Rounding 
  of 
  Sand 
  by 
  Solution. 
  

  

  of 
  acicular 
  crystals, 
  dissolve 
  into 
  bizarre 
  forms 
  bounded 
  

   by 
  curved 
  surfaces. 
  Long 
  crystals 
  or 
  rhombohedral 
  

   fragments 
  as 
  of 
  calcite, 
  produce 
  oval, 
  roller 
  shaped 
  or 
  

   very 
  prolate 
  spheroids. 
  Grains 
  of 
  garnet, 
  magnetite^ 
  

   zircon, 
  apatite, 
  monazite 
  and 
  others 
  which 
  have 
  a 
  com- 
  

   paratively 
  equidimensional 
  crystalline 
  form 
  to 
  start 
  with, 
  

   more 
  rapidly 
  assume 
  or 
  reach 
  a 
  better 
  rounded 
  form 
  than 
  

   more 
  angular 
  crystals, 
  as 
  those 
  of 
  hornblende 
  and 
  feld- 
  

   spars. 
  Mineral 
  grains, 
  including 
  quartz, 
  are 
  often 
  more 
  

   or 
  less 
  round 
  as 
  they 
  occur 
  in 
  the 
  parent 
  igneous 
  or 
  meta- 
  

   morphic 
  rock 
  from 
  which 
  sands 
  are 
  derived. 
  These 
  

   could 
  scarcely 
  be 
  distinguished 
  from 
  grains 
  rounded 
  by 
  

   abrasion 
  or 
  by 
  solution. 
  

  

  There 
  is 
  a 
  tendency 
  in 
  nature 
  for 
  large 
  objects 
  to 
  

   become 
  round 
  due 
  to 
  gravity 
  and 
  for 
  small 
  plastic 
  par- 
  

   ticles 
  to 
  take 
  such 
  form 
  by 
  surface 
  tension, 
  the 
  effects 
  of 
  

   which 
  are 
  universally 
  present 
  in 
  drops 
  or 
  particles 
  of 
  

   liquids. 
  Snow 
  flakes 
  change 
  from 
  flat, 
  radiating 
  crystals 
  

   to 
  subround 
  pellets 
  or 
  "snow 
  sand" 
  without 
  melting, 
  

   probably 
  due 
  to 
  sublimation, 
  as 
  suggested 
  by 
  Cornish. 
  6 
  

   The 
  molecular 
  attraction 
  in 
  minerals 
  of 
  ordinary 
  sands 
  

   is 
  so 
  much 
  greater 
  than 
  surface 
  tension 
  in 
  the 
  same 
  

   minerals 
  that 
  grains 
  of 
  sand 
  do 
  not 
  tend 
  to 
  become 
  round 
  

   in 
  any 
  of 
  these 
  ways. 
  

  

  Motion 
  of 
  grains 
  and 
  solvent. 
  — 
  Grains 
  are 
  more 
  per- 
  

   fectly 
  and 
  more 
  rapidly 
  rounded 
  by 
  solution 
  when 
  they 
  

   are 
  moved 
  about 
  in 
  the 
  liquid, 
  thus 
  allowing 
  the 
  unsat- 
  

   urated 
  solute 
  to 
  come 
  into 
  contact 
  with 
  the 
  grain 
  on 
  all 
  

   sides, 
  and 
  eliminating 
  the 
  factor 
  of 
  diffusion 
  and 
  corro- 
  

   sion. 
  When 
  the 
  grains 
  are 
  not 
  moved, 
  as 
  in 
  the 
  decom- 
  

   posed 
  granites, 
  residual 
  soils, 
  clays 
  and 
  loess 
  which 
  I 
  

   have 
  examined, 
  or 
  in 
  experiments 
  on 
  solution 
  rounding, 
  

   corrosion 
  produces 
  a 
  peculiar 
  texture 
  of 
  the 
  surface 
  not 
  

   like 
  that 
  of 
  abrasion 
  but 
  easily 
  mistaken 
  for 
  it. 
  

  

  Quartz 
  grains 
  washed 
  from 
  Cretaceous 
  clay 
  from 
  Xew 
  

   Jersey, 
  varying 
  in 
  size 
  from 
  -06 
  mm. 
  down 
  to 
  -001 
  mm., 
  are 
  

   not 
  transparent 
  like 
  ordinary 
  quartz 
  but 
  are 
  translucent, 
  

   due 
  to 
  the 
  corroded 
  surfaces. 
  The 
  grains 
  are 
  not 
  sharply 
  

   angular 
  but 
  somewhat 
  roundish 
  in 
  form, 
  and 
  the 
  surfaces 
  

   are 
  not 
  smooth 
  like 
  glass, 
  nor 
  have 
  an 
  even 
  curve 
  and 
  

   "frosted" 
  surface 
  like 
  abraded 
  grains, 
  but 
  have 
  a 
  

   minutely 
  rough 
  surface 
  like 
  rusted 
  iron 
  or 
  weathered 
  

   feldspars. 
  T 
  believe 
  these 
  features 
  were 
  due 
  to 
  slow 
  

  

  "Cornish, 
  Wavos 
  of 
  Sand 
  mid 
  Snow, 
  pp. 
  117-121, 
  1014. 
  

  

  