﻿FIFTH 
  REPORT 
  OF 
  THE 
  DIRECTOR 
  I908 
  

  

  157 
  

  

  feet 
  long 
  and 
  from 
  35 
  to 
  50 
  feet 
  wide 
  was 
  fractured 
  along 
  two 
  

   approximately 
  parallel 
  lines 
  and 
  the 
  included 
  mass 
  dropped 
  a 
  dis- 
  

   tance 
  of 
  fully 
  40 
  feet 
  along 
  the 
  northern 
  fracture 
  plane. 
  This 
  

   plane 
  had 
  a 
  slope 
  of 
  80° 
  toward 
  the 
  ravine. 
  It 
  showed 
  a 
  smooth 
  

   surface 
  against 
  which 
  the 
  sunken 
  block 
  abutted 
  so 
  closely 
  as 
  to 
  

   leave 
  no 
  opening. 
  The 
  walls 
  of 
  the 
  second 
  fracture 
  within 
  the 
  

   ravine 
  inclined 
  away 
  from 
  each 
  other 
  (due 
  to 
  the 
  decided 
  tilt 
  of 
  

   the 
  fallen 
  block 
  toward 
  the 
  north 
  and 
  the 
  upraising 
  of 
  the 
  ad- 
  

   jacent 
  beds) 
  and 
  were 
  separated 
  by 
  a 
  gap 
  15 
  feet 
  wide 
  and 
  nearly 
  

   as 
  deep. 
  

  

  Vertical 
  section 
  across 
  the 
  fault 
  planes. 
  Original 
  slope 
  of 
  hill 
  is 
  indicated 
  by 
  the 
  dotted 
  

   line, 
  while 
  the 
  heavy 
  brokan 
  horizontal 
  line 
  shows 
  the 
  approximite 
  witer 
  le.''3i. 
  

  

  The 
  clay 
  beds 
  behaved 
  very 
  much 
  like 
  solidified 
  rocks. 
  In 
  their 
  

   mass 
  they 
  were 
  but 
  little 
  cracked 
  or 
  disturbed 
  by 
  the 
  subsidence. 
  

   The 
  beds 
  above 
  water 
  level 
  had 
  become 
  fairly 
  dry 
  by 
  evaporation 
  

   and 
  absorption 
  of 
  moisture 
  by 
  plant 
  growth 
  after 
  the 
  spring 
  rains, 
  

   so 
  that 
  at 
  the 
  time 
  of 
  the 
  occurrence 
  they 
  must 
  have 
  been 
  firm 
  

   and 
  tenacious. 
  

  

  The 
  principal 
  factor 
  in 
  determining 
  the 
  nature 
  of 
  the 
  slip 
  was, 
  

   no 
  doubt, 
  the 
  presence 
  of 
  an 
  underlying 
  mass 
  of 
  water-soaked 
  

   semiliquid 
  clay 
  beneath 
  the 
  dry 
  upper 
  beds, 
  approximately 
  fol- 
  

   lowing 
  the 
  level 
  of 
  the 
  stream. 
  Evidence 
  of 
  this 
  liquid 
  clay 
  was 
  

   observed 
  in 
  the 
  lowest 
  part 
  of 
  the 
  ravine 
  where 
  a 
  considerable 
  

   quantity 
  had 
  accumulated 
  by 
  extrusion 
  during 
  the 
  subsidence. 
  

   The 
  upper 
  beds 
  were 
  thus 
  probably 
  in 
  a 
  state 
  of 
  delicate 
  equilib- 
  

   rium, 
  ready 
  to 
  be 
  precipitated 
  from 
  any 
  slight 
  cause 
  which 
  seems 
  

   to 
  have 
  been 
  furnished 
  by 
  opening 
  of 
  the 
  parallel 
  fissures 
  some 
  time 
  

  

  