﻿114 
  OLDHAM: 
  GRE.aT 
  EARTHQUAKE 
  OF 
  1897. 
  

  

  not 
  acquire 
  sufficient 
  momentum 
  to 
  cause 
  it 
  to 
  be 
  detached 
  from 
  the 
  

   underlying 
  rock 
  ; 
  in 
  the 
  latter, 
  the 
  gradual 
  increase 
  in 
  the 
  cohesion 
  

   of 
  the 
  surface 
  layer 
  adhesion 
  to 
  the 
  underlying 
  rock 
  is, 
  more 
  or, 
  and 
  

   in 
  its 
  less, 
  proportionate 
  to 
  the 
  increase 
  of 
  strain 
  applied, 
  and 
  the 
  

   surface 
  layer 
  will 
  be 
  much 
  less 
  liable 
  to 
  come 
  away 
  than 
  if 
  there 
  was 
  

   a 
  more 
  or 
  less 
  well 
  defined 
  plane 
  of 
  weakness. 
  

  

  In 
  the 
  case 
  of 
  sedimentary 
  rocks, 
  the 
  boundary 
  between 
  the 
  

   weathered 
  soilcap 
  and 
  the 
  underlying 
  rock 
  is 
  generally 
  more 
  abrupt 
  

   and 
  the 
  surface 
  layer 
  readily 
  separates 
  from 
  the 
  rock 
  below. 
  Added 
  

   to 
  this 
  the 
  sandstones, 
  which 
  form 
  so 
  large 
  a 
  proportion 
  of 
  the 
  hills 
  

   along 
  the 
  southern 
  face 
  of 
  the 
  range, 
  have 
  a 
  much 
  lower 
  cohesive 
  

   strength 
  than 
  the 
  crystalline 
  and 
  metamorphic 
  rocks 
  of 
  the 
  central 
  

   and 
  northern 
  portions 
  of 
  the 
  range 
  and, 
  when 
  they 
  form 
  high 
  scarps, 
  

   portions 
  of 
  the 
  solid 
  rock 
  itself 
  may 
  be 
  thrown 
  off, 
  

  

  I 
  have 
  thought 
  it 
  necessary 
  to 
  devote 
  some 
  space 
  to 
  a 
  general 
  

   consideration 
  of 
  the 
  causes 
  which 
  are 
  concerned 
  in 
  the 
  formation 
  

   of 
  earthquake-landslips, 
  as 
  very 
  erroneous 
  conclusions 
  have 
  been 
  

   drawn 
  from 
  their 
  distribution, 
  and 
  are 
  generally 
  held 
  in 
  Assam, 
  as 
  to 
  

   the 
  position 
  of 
  the 
  focus 
  of 
  this 
  earthquake. 
  We 
  see 
  that 
  besides 
  

   the 
  energy 
  of 
  the 
  earthquake 
  wave, 
  the 
  production 
  of 
  landslips 
  is 
  

   controlled 
  by 
  the 
  petrological 
  composition 
  of 
  the 
  hill 
  and 
  by 
  another 
  

   factor, 
  into 
  which 
  the 
  angle 
  of 
  slope 
  and 
  the 
  height 
  of 
  the 
  hill 
  enter, 
  

   in 
  other 
  words, 
  by 
  its 
  size 
  and 
  form. 
  It 
  is 
  not 
  possible 
  to 
  express 
  

   mathematically 
  the 
  relative 
  importance 
  of 
  these 
  different 
  factors, 
  the 
  

   nature 
  of 
  their 
  influence 
  can 
  only 
  be 
  pointed 
  out 
  in 
  general 
  terms, 
  

   but 
  it 
  is 
  evident 
  that 
  any 
  conclusion 
  drawn 
  by 
  attributing 
  the 
  whole 
  

   of 
  the 
  effects 
  to 
  only 
  one 
  of 
  the 
  operating 
  causes 
  must 
  necessarily 
  

   lead 
  to 
  error. 
  

  

  After 
  these 
  preliminary 
  remarks 
  we 
  may 
  proceed 
  to 
  a 
  considera- 
  

   tion 
  of 
  the 
  distribution 
  of 
  the 
  landslips 
  and 
  of 
  their 
  effects. 
  In 
  doincr 
  

   this, 
  it 
  is 
  necessary 
  to 
  remember 
  that 
  the 
  observations 
  and 
  informa- 
  

   tion, 
  on 
  which 
  the 
  following 
  passages 
  are 
  based, 
  was 
  obtained 
  some 
  

  

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