﻿FISSUKES 
  AND 
  VENTS. 
  99 
  

  

  In 
  all 
  other 
  cases 
  cranking 
  at 
  one 
  place 
  was 
  always 
  accompanied 
  by 
  tearing- 
  

   at 
  one 
  or 
  other 
  , 
  or 
  on 
  both, 
  sides 
  of 
  the 
  cranked 
  rails, 
  sometimes 
  about 
  80 
  yards 
  

   away, 
  but 
  usually 
  much 
  further, 
  and 
  in 
  a 
  few 
  cases 
  upwards 
  of 
  a 
  quarter 
  of 
  a 
  mile 
  

   away. 
  As 
  a 
  rule, 
  rail 
  joints, 
  when 
  torn, 
  only 
  opened 
  about 
  3" 
  but 
  in 
  some 
  cases 
  

   they 
  opened 
  out 
  considerably 
  more, 
  and 
  in 
  a 
  few 
  instances 
  as 
  much 
  as 
  10* 
  or 
  11". 
  

   I 
  do 
  not 
  remember 
  any 
  case 
  of 
  the 
  rails 
  being 
  torn 
  asunder 
  without 
  cranking 
  

   occurring 
  in 
  the 
  vicinity." 
  

  

  From 
  these 
  statements 
  it 
  is 
  obvious 
  that 
  the 
  shortening 
  of 
  the 
  

  

  rails 
  does 
  not 
  necessarily 
  indicate 
  any 
  general 
  compression, 
  and 
  that 
  

  

  it 
  is 
  rather 
  to 
  be 
  attributed 
  to 
  local 
  displacements 
  of 
  the 
  alluvium, 
  

  

  whereby 
  a 
  compression 
  in 
  one 
  place 
  is 
  compensated 
  by 
  an 
  expansion 
  

  

  elsewhere, 
  and 
  generally 
  at 
  about 
  300 
  yards 
  away. 
  

  

  So 
  far 
  I 
  have 
  considered 
  only 
  the 
  effects 
  of 
  the 
  horizontal 
  com* 
  

   ponent 
  of 
  the 
  wave 
  motion, 
  or 
  at 
  any 
  rate, 
  the 
  effects 
  which 
  might 
  

   have 
  been 
  produced 
  had 
  there 
  been 
  no 
  vertical 
  component 
  of 
  the 
  wave 
  

   motion. 
  We 
  now 
  come 
  to 
  the 
  consideration 
  of 
  those 
  effects 
  which 
  can 
  

   only 
  be 
  explained 
  by 
  supposing 
  that 
  the 
  wave 
  motion 
  had 
  a 
  vertical 
  

   component, 
  in 
  other 
  words, 
  that 
  the 
  movement 
  of 
  the 
  wave 
  particle 
  

   was 
  to 
  a 
  certain 
  extent 
  up 
  and 
  down 
  as 
  well 
  as 
  from 
  side 
  to 
  side. 
  

  

  First 
  of 
  these 
  come 
  the 
  sand 
  vents, 
  and 
  the 
  first 
  thing 
  to 
  be 
  

   noticed 
  is 
  that 
  in 
  some 
  cases 
  they 
  were 
  not 
  formed 
  till 
  after 
  the 
  

   earthquake 
  shock 
  had 
  passed 
  away. 
  On 
  this 
  point 
  the 
  evidence 
  of 
  

   Mr. 
  D. 
  R. 
  Lyall's 
  account 
  is 
  decisive 
  in 
  itself 
  1 
  , 
  and 
  a 
  similar 
  statement, 
  

   to 
  be 
  found 
  in 
  the 
  reports 
  of 
  Captain 
  Gurdon 
  and 
  of 
  the 
  Magistrate 
  

   of 
  Bogra, 
  who 
  records 
  that 
  the 
  bhorkas 
  or 
  sand 
  craters 
  appeared 
  after 
  

   the 
  earthquake 
  had 
  ceased 
  2 
  . 
  

  

  This 
  appearance 
  of 
  sand 
  vents, 
  after 
  the 
  actual 
  movement 
  of 
  the 
  

   earthquake 
  wave 
  had 
  passed 
  away, 
  is 
  easily 
  explicable, 
  as 
  the 
  result 
  

   of 
  the 
  momentum 
  imparted 
  to 
  the 
  water 
  bearing 
  stratum, 
  a 
  momenture 
  

   which 
  could 
  not 
  be 
  immediately 
  absorbed, 
  and 
  was 
  in 
  some 
  cases 
  

   sufficient 
  to 
  force 
  the 
  sand 
  and 
  water 
  through 
  the 
  overlying 
  beds 
  

   weakened, 
  as 
  they 
  doubtless 
  were 
  in 
  places, 
  by 
  the 
  earthquake 
  which 
  

   had 
  passed 
  away. 
  

  

  1 
  See 
  p. 
  26. 
  2 
  See 
  Appendix 
  B 
  

  

  H 
  2 
  ( 
  99 
  ) 
  

  

  