﻿368 
  OLDHAM 
  : 
  GREAT 
  EARTHQUAKE 
  OK 
  1897. 
  

  

  Himalayas 
  are 
  the 
  leading 
  types, 
  there 
  are 
  mountains 
  of 
  faulting, 
  the 
  ' 
  Schollen- 
  

   gebirge' 
  of 
  German, 
  and 
  ' 
  block 
  mountains' 
  of 
  American, 
  geologists. 
  In 
  these 
  

   the 
  relief 
  is 
  directly 
  due 
  to 
  movements 
  along 
  the 
  lines 
  of 
  faulting 
  by 
  which 
  the 
  

   rocks 
  are 
  traversed, 
  and 
  the 
  principal 
  crests 
  and 
  steepest 
  slopes, 
  though 
  modified 
  

   by 
  subsequent 
  denudation, 
  follow 
  and 
  are 
  due 
  to 
  these 
  lines 
  of 
  fault. 
  

  

  In 
  the 
  case 
  of 
  hills 
  of 
  this 
  type, 
  their 
  elevation 
  far 
  from 
  having 
  been 
  due 
  to 
  com- 
  

   pression, 
  has 
  been 
  accompanied 
  by 
  an 
  actual 
  extension 
  of 
  the 
  ground 
  they 
  cover. 
  

   The 
  faults 
  are 
  vertical 
  or 
  normal 
  and 
  the 
  horizontal 
  distance 
  between 
  two 
  points 
  

   on 
  either 
  side 
  of 
  the 
  fault, 
  is 
  greater 
  after, 
  than 
  it 
  was 
  before, 
  the 
  elevation. 
  The 
  

   mechanism 
  of 
  the 
  formation 
  of 
  these 
  mountains 
  of 
  faulting 
  is 
  not 
  very 
  easy 
  to 
  

   understand; 
  it 
  may 
  be 
  that 
  the 
  faulting 
  and 
  stretching 
  are 
  confined 
  to 
  the 
  upper 
  

   layers 
  of 
  rock 
  and 
  are 
  indirect 
  results 
  of 
  a 
  compression, 
  and 
  consequent 
  thickening 
  

   of 
  the 
  more 
  deep 
  seated 
  layers, 
  through 
  the 
  small 
  depth 
  at 
  which 
  the 
  level 
  of 
  no 
  

   strain 
  is 
  placed 
  makes 
  this 
  supposition 
  difficult 
  of 
  acceptance. 
  A 
  more 
  probable 
  

   explanation 
  is 
  that 
  over 
  certain 
  areas 
  the 
  upper 
  layers 
  are 
  protected 
  from 
  that 
  

   compression 
  which 
  is 
  their 
  general 
  fate, 
  and 
  follow 
  the 
  movements 
  of 
  the 
  rocks 
  

   below 
  the 
  level 
  of 
  no 
  strain, 
  which 
  are 
  being 
  stretched. 
  The 
  tension 
  thus 
  set 
  up 
  in 
  

   the 
  rocks 
  above 
  the 
  level 
  of 
  no 
  strain 
  would 
  cause 
  them 
  to 
  be 
  split 
  by 
  vertical 
  or 
  

   highly 
  inclined 
  fractures, 
  and 
  the 
  horizontal 
  extension 
  would 
  be 
  taken 
  up 
  by 
  sub- 
  

   sidence 
  along 
  these. 
  

  

  Whatever 
  may 
  be 
  the 
  explanation, 
  the 
  facts 
  are 
  undoubted, 
  and 
  it 
  is 
  conceiv- 
  

   able, 
  though 
  with 
  difficulty, 
  that 
  in 
  such 
  a 
  region 
  tensional 
  strains 
  might 
  be 
  set 
  up 
  

   of 
  sufficient 
  greatness 
  to 
  give 
  rise 
  to 
  a 
  severe 
  earthquake 
  by 
  their 
  sudden 
  relief. 
  

   The 
  Assam 
  range 
  presents 
  the 
  superficial 
  features 
  of 
  a 
  region 
  of 
  mountains 
  of 
  the 
  

   character 
  just 
  considered, 
  and 
  it 
  may 
  be 
  that 
  the 
  explanation 
  of 
  the 
  fault 
  scarps 
  

   is 
  not 
  that 
  offered 
  in 
  Chapter 
  X. 
  Possibly 
  the 
  elevation 
  of 
  the 
  range 
  was 
  accom- 
  

   panied 
  by 
  extension 
  and 
  not 
  by 
  compression, 
  and 
  in 
  that 
  case 
  the 
  apparent 
  ex- 
  

   tension, 
  exhibited 
  by 
  the 
  results 
  of 
  the 
  retriangulation, 
  would 
  be 
  in 
  accordance 
  with 
  

   what 
  should 
  be 
  expected. 
  The 
  small 
  changes, 
  exhibited 
  by 
  the 
  southern 
  triangles 
  

   would 
  be 
  explained 
  b)> 
  the 
  absence 
  of 
  fault 
  scarps 
  in 
  that 
  region, 
  while 
  the 
  great 
  

   changes 
  of 
  horizontal 
  distance, 
  as 
  well 
  as 
  of 
  elevation, 
  in 
  the 
  northern 
  triangles 
  

   would 
  be 
  explained 
  by 
  the 
  number 
  of 
  fault 
  scarps 
  seen 
  in 
  the 
  region 
  they 
  cover. 
  

  

  If 
  this 
  explanation 
  is 
  adopted 
  it 
  would 
  cause 
  no 
  change 
  in 
  the 
  conclusions 
  

   stated 
  in 
  Chapter 
  X 
  as 
  to 
  the 
  position, 
  the 
  complexity 
  or 
  the 
  extent 
  of 
  the 
  seismic 
  

   focus 
  regarded 
  as 
  a 
  whole, 
  but 
  the 
  assumed 
  thrust 
  plane 
  or 
  planes, 
  uniting 
  the 
  

   complex 
  of 
  more 
  superficial 
  fractures 
  and 
  faults, 
  would 
  not 
  exist, 
  and 
  the 
  strain 
  to 
  

   whose 
  relief 
  the 
  earthquake 
  was 
  due 
  would 
  be 
  one 
  of 
  tension 
  and 
  not 
  compres- 
  

   sion. 
  In 
  other 
  words 
  it 
  would 
  cause 
  no 
  change 
  in 
  what 
  can 
  be 
  directly 
  determined 
  

   from 
  observed 
  facts, 
  though 
  some 
  change 
  may 
  be 
  necessary 
  in 
  the 
  more 
  remote 
  

   deductions 
  as 
  to 
  the 
  ultimate 
  cause 
  of 
  the 
  earthquake. 
  

  

  1 
  It 
  would 
  also 
  make 
  the 
  faults, 
  to 
  which 
  the 
  fault 
  scarps 
  of 
  the 
  Assam 
  range 
  are 
  due, 
  

   normal 
  and 
  not 
  reversed 
  faults, 
  and 
  the 
  great 
  monoclinal 
  fold 
  along 
  their 
  southern 
  edge 
  a 
  

   flexure, 
  in 
  the 
  restricted 
  sense 
  in 
  which 
  the 
  word 
  is 
  employed 
  by 
  Suess, 
  and 
  not 
  a 
  fold. 
  The 
  

   distinction 
  being 
  that 
  a 
  fold 
  is 
  the 
  result 
  of 
  compression, 
  a 
  flexure 
  of 
  differential 
  elevation 
  on 
  

   either 
  side 
  of 
  the 
  disturbed 
  tract. 
  As 
  a 
  consequence 
  the 
  distance 
  between 
  two 
  points 
  in 
  any 
  

   given 
  bed, 
  situated 
  on 
  either 
  side 
  of 
  the 
  fold 
  or 
  flexure, 
  will 
  be 
  less 
  than 
  the 
  original 
  distance 
  

   in 
  the 
  case 
  of 
  a 
  fold, 
  greater 
  in 
  that 
  of 
  a 
  flexure. 
  

  

  ( 
  . 
  368 
  ) 
  

  

  