﻿Galloway 
  — 
  Hounding 
  of 
  Sand 
  by 
  Solution. 
  271 
  

  

  "The 
  quartz 
  in 
  quartzose 
  felsites 
  is 
  often 
  of 
  much 
  more 
  truly 
  

   crystalline 
  form, 
  the 
  planes 
  being 
  sometimes 
  very 
  perfect; 
  but 
  

   very 
  often 
  there 
  is 
  a 
  remarkable 
  rounding 
  of 
  the 
  angles, 
  which 
  

   might 
  easily 
  lead 
  any 
  one 
  to 
  think 
  that 
  they 
  were 
  waterworn. 
  

   Even 
  the 
  grains 
  of 
  quartz 
  derived 
  from 
  granite 
  sometimes 
  show 
  

   this 
  character 
  to 
  a 
  less 
  extent, 
  but 
  the 
  rounding 
  is 
  usually 
  accom- 
  

   panied 
  by 
  small 
  surface 
  ridges, 
  which 
  clearly 
  show 
  that 
  their 
  

   rounded 
  form 
  was 
  not 
  due 
  to 
  mechanical 
  wearing. 
  In 
  the 
  speci- 
  

   mens 
  of 
  decomposed 
  granite 
  which 
  I 
  have 
  examined 
  in 
  greatest 
  

   detail, 
  the 
  larger 
  grains 
  of 
  quartz 
  have 
  a 
  somewhat 
  opaque 
  sur- 
  

   face, 
  as 
  if 
  corroded, 
  and 
  the 
  angles 
  are 
  rounded. 
  This 
  rounding 
  

   is 
  relatively 
  much 
  greater 
  in 
  the 
  case 
  of 
  the 
  smaller 
  grains, 
  

   which 
  is 
  the 
  reverse 
  of 
  what 
  is 
  met 
  with 
  in 
  worn 
  sand. 
  On 
  the 
  

   whole 
  the 
  facts 
  seem 
  to 
  indicate 
  that 
  the 
  quartz 
  has 
  been 
  more 
  

   or 
  less 
  corroded 
  and 
  dissolved 
  by 
  the 
  action 
  of 
  the 
  alkaline 
  sili- 
  

   cates 
  set 
  free 
  by 
  the 
  decomposition 
  of 
  the 
  feldspar. 
  The 
  con- 
  

   trast 
  between 
  its 
  corroded 
  surface 
  and 
  the 
  glassy 
  fractures 
  of 
  

   broken 
  quartz 
  is 
  very 
  great." 
  

  

  A 
  few 
  simple 
  experiments 
  will 
  demonstrate 
  that 
  crys- 
  

   tals 
  or 
  mineral 
  fragments 
  of 
  any 
  shape 
  tend 
  to 
  become 
  

   round 
  in 
  the 
  process 
  of 
  dissolving. 
  

  

  If 
  a 
  pinch 
  of 
  sodium 
  chloride, 
  potassium 
  chloride, 
  

   sugar 
  or 
  any 
  other 
  finely 
  granular 
  material, 
  which 
  is 
  

   readily 
  soluble 
  in 
  water 
  is 
  put 
  into 
  a 
  few 
  drops 
  of 
  water 
  

   on 
  a 
  slide 
  and 
  observed 
  under 
  a 
  microscope, 
  the 
  angular 
  

   grains 
  will 
  be 
  seen 
  to 
  change 
  to 
  rounded 
  ones 
  by 
  the 
  more 
  

   rapid 
  dissolving 
  of 
  the 
  corners. 
  The 
  smaller 
  the 
  grains 
  

   become 
  the 
  more 
  nearly 
  spherical 
  they 
  become. 
  If 
  

   ground 
  calcite, 
  or 
  any 
  other 
  finely 
  granular, 
  pure, 
  crystal- 
  

   line 
  material 
  is 
  partially 
  dissolved 
  in 
  acid, 
  the 
  grains 
  will 
  

   be 
  rounded 
  by 
  solution. 
  Fig. 
  1 
  shows 
  the 
  forms 
  and 
  

   character 
  of 
  surface 
  produced 
  when 
  grains 
  of 
  Iceland 
  

   spar 
  are 
  partially 
  dissolved 
  in 
  warm 
  hydrochloric 
  acid. 
  

  

  As 
  is 
  well 
  known, 
  all 
  the 
  minerals 
  occurring 
  in 
  sands 
  

   are 
  soluble 
  in 
  natural 
  waters. 
  The 
  process 
  is 
  accelerated 
  

   when 
  the 
  water 
  contains 
  appreciable 
  quantities 
  of 
  alkalis 
  

   or 
  acids. 
  The 
  feldspars 
  and 
  ferromagnesian 
  minerals 
  

   dissolve 
  fairly 
  readily. 
  Quartz, 
  magnetite, 
  rutile, 
  zircon, 
  

   apatite, 
  garnet, 
  muscovite 
  and 
  monazite 
  are 
  extremely 
  

   resistant 
  to 
  solution, 
  but 
  even 
  these 
  may 
  be 
  dissolved 
  

   naturally 
  in 
  water 
  when 
  the 
  amount 
  of 
  water 
  and 
  time 
  

   are 
  great 
  enough. 
  4 
  

  

  The 
  physical 
  process 
  involved 
  in 
  the 
  rounding 
  of 
  small 
  

  

  4 
  See 
  Clarke, 
  Data 
  of 
  Geochemistry, 
  U. 
  S. 
  G. 
  S., 
  Bull. 
  616, 
  pp. 
  478-483, 
  

   1916; 
  Merrill, 
  Kocks, 
  Eock 
  Weathering- 
  and 
  Soils, 
  pp. 
  189-194, 
  236-238; 
  

   Van 
  Hise. 
  Treatise 
  on 
  Metamorphism, 
  IT. 
  S. 
  G. 
  S., 
  Mon. 
  47, 
  pp. 
  516, 
  848, 
  

   1904. 
  

  

  