﻿344 
  1. 
  0. 
  Russell 
  — 
  "Plasticity" 
  of 
  Glacial 
  Ice. 
  

  

  Art. 
  XXXIII.— 
  A 
  Note 
  on 
  the 
  "Plasticity" 
  of 
  Glacial 
  Ice; 
  

   by 
  Israel 
  C. 
  Russell. 
  

  

  It 
  is 
  conceded, 
  I 
  think, 
  by 
  all 
  students 
  of 
  glacial 
  phenomena, 
  

   that 
  the 
  flow 
  of 
  glaciers 
  is 
  at 
  least 
  analogous 
  to 
  the 
  flow 
  of 
  

   plastic 
  solids 
  under 
  the 
  influence 
  of 
  gravity. 
  That 
  the 
  flow 
  of 
  

   glaciers 
  is 
  due 
  to 
  true 
  plasticity, 
  however, 
  as 
  claimed 
  by 
  Forbes 
  

   and 
  others, 
  cannot 
  be 
  admitted 
  in 
  view 
  of 
  somewhat 
  recent 
  

   experiments 
  on 
  the 
  bending 
  of 
  ice 
  by 
  McConnell, 
  Kidd 
  and 
  

   Miigge.* 
  

  

  These 
  experiments 
  have 
  demonstrated 
  that 
  a 
  bar 
  of 
  ice 
  cut 
  

   from 
  a 
  single 
  crystal, 
  with 
  the 
  optic 
  axis 
  perpendicular 
  to 
  two 
  

   of 
  the 
  side 
  faces, 
  when 
  subjected 
  to 
  a 
  bending 
  stress, 
  will 
  bend 
  

   freely 
  in 
  the 
  plane 
  of 
  the 
  optic 
  axis, 
  but 
  not 
  at 
  all 
  in 
  a 
  plane 
  

   perpendicular 
  to 
  that 
  axis. 
  In 
  the 
  bent 
  crystals 
  the 
  optic 
  axis 
  

   in 
  any 
  part 
  is 
  normal 
  to 
  the 
  bent 
  face 
  in 
  that 
  part. 
  As 
  stated 
  

   by 
  McConnell, 
  a 
  crystal 
  when 
  thus 
  tested 
  behaves 
  as 
  if 
  it 
  were 
  

   composed 
  of 
  an 
  infinite 
  number 
  of 
  thin 
  sheets 
  of 
  paper, 
  normal 
  

   to 
  its 
  optic 
  axis, 
  and 
  attached 
  to 
  each 
  other 
  by 
  some 
  viscous 
  sub- 
  

   stance 
  which 
  allowed 
  one 
  to 
  slide 
  over 
  the 
  next 
  with 
  great 
  diffi- 
  

   culty. 
  The 
  greatest 
  freedom 
  of 
  movement 
  was 
  found 
  to 
  occur 
  

   when 
  the 
  ice 
  experimented 
  on 
  was 
  near 
  the 
  melting 
  point, 
  and 
  

   became 
  less 
  and 
  less 
  with 
  a 
  decrease 
  of 
  temperature. 
  In 
  cer- 
  

   tain 
  of 
  the 
  experiments 
  referred 
  to, 
  the 
  freedom 
  of 
  movement 
  

   at 
  —2° 
  C. 
  was 
  twice 
  as 
  great 
  as 
  at 
  —10° 
  C. 
  

  

  These 
  experiments 
  seem 
  to 
  furnish 
  an 
  explanation 
  of 
  some 
  

   of 
  the 
  phases 
  of 
  glacial 
  motion, 
  and 
  of 
  the 
  growth 
  of 
  the 
  

   granules 
  of 
  glacial 
  ice. 
  When 
  thin 
  sections 
  of 
  glacial 
  ice 
  are 
  

   examined 
  by 
  means 
  of 
  polarized 
  light,f 
  it 
  is 
  seen 
  that 
  the 
  

   granules 
  of 
  which 
  it 
  is 
  composed 
  are 
  fragments 
  of 
  ice 
  crystals, 
  

   or 
  perhaps 
  imperfectly 
  formed 
  crystals, 
  which 
  interlock 
  one 
  

   with 
  another 
  so 
  that 
  the 
  structure 
  resembles 
  that 
  of 
  coarsely 
  

   crystalline 
  dolomite. 
  

  

  The 
  optic 
  axes 
  of 
  the 
  granules 
  are 
  without 
  orderly 
  arrange- 
  

   ment, 
  but 
  have 
  all 
  directions. 
  Pressure 
  brought 
  to 
  bear 
  on 
  

   such 
  granular 
  ice 
  in 
  a 
  definite 
  direction, 
  would 
  cause 
  move- 
  

   ment 
  in 
  the 
  crystal 
  fragments 
  or 
  granules, 
  whose 
  optic 
  axes 
  

   were 
  in 
  the 
  plane 
  of 
  pressure, 
  but 
  would 
  not 
  change 
  the 
  forms 
  

   of 
  the 
  crystal 
  fragments 
  not 
  thus 
  oriented. 
  The 
  crystal 
  frag- 
  

  

  * 
  J. 
  C. 
  McConnell 
  and 
  D. 
  A. 
  Kidd: 
  " 
  On 
  the 
  plasticity 
  of 
  glacial 
  and 
  other 
  ice," 
  

   Roy. 
  Soc. 
  London. 
  Proa, 
  vol. 
  xliv, 
  1883, 
  pp 
  131-161. 
  J. 
  C. 
  McConnell: 
  "On 
  the 
  

   plasticity 
  of 
  an 
  ice 
  crystal," 
  ibid., 
  vol. 
  xlviii, 
  1890, 
  pp. 
  256-260 
  ; 
  vol. 
  xlix, 
  1891, 
  

   pp. 
  323-343. 
  0. 
  Mugge: 
  " 
  Ueber 
  die 
  Plasticitat 
  der 
  Eiskrystalle," 
  Separat- 
  

   Abdruck 
  aus 
  dem 
  Neuen 
  Jahrbuch 
  fur 
  Mineralogie, 
  etc 
  , 
  1895, 
  Bd. 
  II, 
  cited 
  in 
  

   the 
  Journal 
  of 
  Geology, 
  vol. 
  iii, 
  1895, 
  pp 
  965, 
  966. 
  

  

  \ 
  R. 
  M. 
  Deeley 
  an-1 
  George 
  Fletcher: 
  "The 
  structure 
  of 
  glacial 
  ice 
  and 
  its 
  

   bearing 
  upon 
  glacial 
  motion," 
  Geol. 
  Mag. 
  (London), 
  Decade 
  4, 
  vol. 
  ii, 
  1895, 
  pp. 
  

   152-162. 
  

  

  