﻿32 
  

  

  FEDDEN 
  : 
  GEOLOGY 
  OF 
  KATHIAWAR 
  PENINSULA 
  IN 
  GUZERAT, 
  

  

  Other 
  evidences 
  of 
  great 
  compression, 
  and 
  vertical 
  motion, 
  are 
  dis- 
  

   played 
  in 
  the 
  up-tnrned 
  edges 
  of 
  the 
  adjacent 
  beds, 
  not 
  unfrequently 
  seen 
  

   on 
  one 
  or 
  other 
  side 
  of 
  the 
  dyke, 
  as 
  shown 
  in 
  the 
  accompanying 
  sketch 
  

   section. 
  

  

  Sketch 
  Section 
  

   CL. 
  By~kjz 
  . 
  B. 
  SctTuLsijorie. 
  

  

  The 
  effect 
  of 
  a 
  dyke, 
  on 
  the 
  sedimentary 
  beds 
  traversed, 
  is 
  generally 
  

   to 
  indurate, 
  and 
  at 
  times 
  to 
  blacken 
  or 
  to 
  bleach 
  the 
  rock 
  for 
  a 
  short 
  way 
  

   on 
  either 
  side 
  : 
  and 
  the 
  hardened 
  portion, 
  being 
  the 
  better 
  able 
  to 
  resist 
  

   denudation, 
  often 
  remains 
  as 
  a 
  narrow 
  craggy 
  ridge 
  along 
  the 
  course 
  of 
  

   the 
  dyke. 
  This 
  feature, 
  together 
  with 
  that 
  of 
  the 
  upturned 
  edge 
  of 
  the 
  

   wall-rock, 
  enables 
  one 
  to 
  trace 
  the 
  course 
  of 
  a 
  dyke, 
  even 
  when 
  no 
  trap 
  is 
  

   visible 
  on 
  the 
  surface. 
  

  

  The 
  dyke-trap 
  in 
  this 
  part 
  of 
  the 
  field 
  is 
  almost 
  invariably 
  either 
  a 
  

   fine-grained 
  compact 
  blue-black 
  basalt, 
  or 
  otherwise 
  is 
  in 
  the 
  decomposed 
  

   state 
  of 
  ' 
  wache 
  3 
  ; 
  it 
  is 
  never 
  largely 
  crystalline 
  nor 
  porphyritic, 
  as 
  many 
  

  

  Dykes 
  transversely 
  col- 
  of 
  tne 
  bedded 
  floWS 
  are 
  « 
  < 
  The 
  baSalt 
  ° 
  f 
  the 
  d 
  J 
  keS 
  > 
  

   umnar. 
  as 
  previously 
  stated, 
  is 
  usually 
  columnar, 
  the 
  

  

  prisms 
  lying 
  horizontally, 
  and 
  transverse 
  to 
  the 
  direction 
  of 
  the 
  course, 
  

  

  i.e., 
  at 
  right 
  angles 
  to 
  the 
  walls, 
  and 
  in 
  the 
  line 
  of 
  greatest 
  resistance 
  ; 
  

  

  whereas 
  the 
  prisms 
  of 
  bedded 
  columnar 
  trap 
  are 
  generally 
  at 
  right 
  

  

  angles 
  to 
  the 
  bedding. 
  

  

  In 
  the 
  broader 
  dykes 
  the 
  trap 
  may 
  be 
  columnar 
  on 
  either 
  side, 
  and 
  

  

  decomposed 
  in 
  the 
  middle, 
  or 
  vice 
  versa. 
  This 
  transversely 
  columnar 
  

  

  structure 
  bef*xg 
  peculiar, 
  enables 
  one 
  to 
  detect 
  a 
  dyke 
  and 
  note 
  its 
  

  

  direction 
  when 
  thenp 
  may 
  be 
  no 
  other 
  indications. 
  

  

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  104 
  ) 
  

  

  

  