﻿134 
  OLDHAM 
  : 
  GREAT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  destructive 
  earthquake 
  waves 
  are 
  confined 
  to 
  the 
  surface, 
  and 
  how 
  a 
  

   trench 
  of 
  only 
  20 
  ft. 
  deep 
  is 
  sufficient 
  to 
  cut 
  them 
  off 
  and 
  protect 
  a 
  

   building 
  by 
  which 
  it 
  is 
  surrounded. 
  In 
  the 
  case 
  of 
  Peacock 
  Island, 
  

   the 
  channel 
  of 
  the 
  Brahmaputra 
  served 
  as 
  a 
  protection 
  against 
  

   earthquakes, 
  at 
  any 
  rate 
  against 
  those 
  which 
  originated 
  at 
  a 
  distance 
  

   and 
  were 
  travelling 
  nearly 
  horizontally. 
  The 
  surface 
  waves 
  were 
  

   exhausted 
  against 
  the 
  edge 
  of 
  the 
  river 
  bank, 
  and 
  the 
  main 
  wave, 
  

   passing 
  under 
  the 
  channel 
  of 
  the 
  Brahmaputra, 
  left 
  the 
  island, 
  as 
  it 
  

   were, 
  in 
  a 
  shadow 
  and 
  protected 
  from 
  anything 
  but 
  an 
  insignificant 
  

   tremor. 
  

  

  The 
  great 
  earthquake 
  of 
  1897, 
  however, 
  instead 
  of 
  reaching 
  

   Gauhati 
  from 
  a 
  distance, 
  was 
  travelling 
  upwards 
  from 
  below. 
  The 
  

   bed 
  of 
  the 
  Brahmaputra 
  consequently 
  gave 
  no 
  protection, 
  and 
  the 
  

   temples 
  on 
  Peacock 
  Island 
  suffered 
  as 
  severely 
  as 
  those 
  on 
  either 
  

   bank 
  of 
  the 
  river. 
  

  

  Before 
  proceeding 
  to 
  a 
  consideration 
  of 
  the 
  permanent 
  changes, 
  

   which 
  accompanied 
  this 
  earthquake, 
  it 
  will 
  be 
  well 
  to 
  describe 
  briefly 
  

   the 
  physical 
  geography 
  and 
  structure 
  of 
  the 
  country 
  involved. 
  The 
  

   group 
  of 
  hills 
  lying 
  south 
  of 
  the 
  Brahmaputra 
  Valley 
  is 
  com- 
  

   monly 
  known 
  in 
  different 
  parts 
  by 
  names 
  derived 
  from 
  the 
  tribes 
  in- 
  

   habiting 
  it, 
  but 
  no 
  general 
  name 
  has 
  found 
  its 
  way 
  on 
  to 
  maps. 
  

   In 
  previous 
  publications 
  of 
  this 
  Survey 
  the 
  names 
  of 
  Shillong 
  plateau 
  

   and 
  Assam 
  range 
  have 
  been 
  proposed 
  and 
  used, 
  and 
  of 
  these 
  the 
  

   former 
  is 
  the 
  most 
  descriptive 
  of 
  its 
  character, 
  the 
  latter 
  most 
  con- 
  

   venient 
  for 
  general 
  use. 
  It 
  is 
  an 
  elevated 
  tract 
  composed 
  of 
  cry- 
  

   stalline 
  gneissic 
  and 
  granitic 
  rocks, 
  with 
  some 
  metamorphic 
  schists 
  

   and 
  quartzite, 
  which 
  carries 
  a 
  varying 
  thickness 
  of 
  cretaceous 
  and 
  

   tertiary 
  rocks 
  along 
  its 
  southern 
  edge. 
  These 
  newer 
  beds 
  thin 
  out 
  

   to 
  the 
  north, 
  not 
  by 
  denudation 
  but 
  by 
  an 
  original 
  thinning 
  out 
  

   due 
  to 
  deposition 
  on 
  a 
  sloping 
  sea 
  bottom. 
  For 
  about 
  50 
  miles, 
  

   along 
  the 
  north 
  of 
  the 
  Sylhet 
  plain, 
  this 
  hilly 
  region 
  ends 
  abruptly 
  

   in 
  a 
  uniclinal 
  flexure 
  or 
  as 
  faulted 
  scarp. 
  At 
  its 
  western 
  end 
  

  

  ( 
  134) 
  

  

  