﻿FISSURES 
  AND 
  VENTS. 
  Ill 
  

  

  the 
  Himalayas, 
  which 
  not 
  only 
  limits 
  the 
  area 
  over 
  which 
  the 
  formation 
  

   of 
  fissures 
  and 
  vents 
  could 
  be 
  possible, 
  but 
  places 
  an 
  absolute 
  barrier 
  

   against 
  the 
  acquisition 
  of 
  any 
  information 
  as 
  to 
  the 
  effect 
  of 
  the 
  

   earthquake 
  in 
  that 
  direction. 
  

  

  Chapter 
  VII.— 
  THE 
  LANDSLIPS. 
  

  

  Landslips 
  were 
  caused 
  by 
  the 
  earthquake 
  on 
  an 
  enormous 
  scale, 
  

   and 
  deserve 
  a 
  special 
  notice, 
  both 
  as 
  to 
  their 
  origin 
  and 
  distribution. 
  

  

  The 
  cause 
  of 
  the 
  landslips 
  is 
  not 
  difficult 
  of 
  explanation. 
  In 
  

   fig. 
  13 
  let 
  the 
  shaded 
  portion 
  represent 
  the 
  solid 
  rock 
  of 
  a 
  hill, 
  drawn 
  

  

  Fig. 
  13. 
  Diagram 
  to 
  illustrate 
  the 
  formation 
  of 
  landslips. 
  

  

  in 
  section, 
  covered 
  by 
  the 
  soilcap 
  O 
  O 
  which 
  is 
  kept 
  in 
  place 
  on 
  the 
  

   underlying 
  reck 
  by 
  the 
  friction 
  between 
  them. 
  When 
  the 
  rock 
  of 
  

   this 
  hill 
  is 
  set 
  into 
  elastic 
  vibration 
  by 
  the 
  earthquake 
  wave, 
  the 
  

   superficial 
  portion 
  will, 
  at 
  one 
  period 
  or 
  other 
  of 
  the 
  shock, 
  be 
  set 
  in 
  

   movement 
  outwards, 
  and 
  this 
  movement 
  will 
  be 
  communicated 
  to 
  the 
  

   soilcap. 
  In 
  the 
  next 
  semiphase 
  of 
  the 
  wave, 
  the 
  movement 
  of 
  the 
  

   surface 
  of 
  the 
  rock 
  will 
  be 
  inwards, 
  but 
  the 
  inertia 
  of 
  the 
  overlying 
  

   soilcap 
  will 
  prevent 
  this 
  following 
  at 
  once, 
  and 
  the 
  effect 
  will 
  be 
  a 
  

   more 
  or 
  less 
  complete 
  reduction 
  of 
  the 
  pressure 
  of 
  the 
  soilcap 
  on 
  the 
  

   rock. 
  This 
  reduction 
  of 
  pressure 
  means 
  a 
  reduction 
  of 
  the 
  friction, 
  

   which 
  alone 
  prevents 
  the 
  soilcap 
  from 
  sliding 
  bodily 
  down 
  the 
  hill, 
  

   and 
  so 
  a 
  landslip 
  is 
  formed, 
  where 
  the 
  reduction 
  of 
  resistance, 
  and 
  the 
  

   slope 
  of 
  the 
  hill, 
  are 
  sufficient 
  to 
  allow 
  of 
  it. 
  In 
  cases 
  where 
  the 
  

  

  ( 
  "i 
  > 
  

  

  