﻿56 
  BOSE 
  : 
  GEOLOGY 
  OF 
  THE 
  LOWER 
  NARBADA 
  VALLEY. 
  

  

  colours 
  (not 
  in 
  bands) 
  are 
  exhibited 
  by 
  the 
  clearer 
  portions. 
  The 
  mineral 
  

   is 
  probably 
  felspar. 
  The 
  heat 
  from 
  the 
  dyke 
  must 
  have 
  partially 
  fused 
  

   the 
  felsitic 
  rock 
  ; 
  the 
  quartz 
  managed 
  to 
  survive, 
  though 
  considerably 
  

   injured; 
  the 
  other 
  minerals 
  succumbed 
  and 
  were 
  melted. 
  The 
  doubtful 
  

   mineral 
  (probably 
  felspathic), 
  described 
  above 
  in 
  detail, 
  crystallised 
  out 
  

   of 
  the 
  molten 
  mass 
  under 
  considerable 
  pressure 
  no 
  doubt, 
  but 
  rather 
  

   quickly, 
  as 
  is 
  evidenced 
  by 
  the 
  numerous 
  stone 
  enclosures. 
  The 
  country 
  

   about 
  Mandlesar, 
  like 
  the 
  rest 
  of 
  the 
  trap 
  country, 
  was 
  quickly 
  traversed, 
  

   and 
  a 
  closer 
  examination 
  may 
  result 
  in 
  the 
  discovery 
  of 
  more 
  dykes 
  or 
  

   branches 
  of 
  the 
  dyke 
  described 
  in 
  the 
  preceding 
  paragraphs. 
  The 
  huge- 
  

   ness 
  of 
  the 
  blocks 
  carried 
  up 
  by 
  it, 
  and 
  the 
  manner 
  in 
  which 
  they 
  have 
  

   been 
  altered 
  prove 
  the 
  intensity 
  of 
  the 
  igneous 
  force 
  at 
  the 
  place, 
  and 
  a 
  

   volcanic 
  centre 
  was 
  probably 
  at 
  hand. 
  This 
  supposition 
  receives 
  confirm- 
  

   ation 
  from 
  the 
  thickness 
  of 
  the 
  ash-beds 
  below 
  Jam 
  Ghat, 
  a 
  few 
  miles 
  

   north 
  of 
  Mandlesar, 
  though 
  the 
  ash 
  is 
  fine-grained, 
  and 
  may 
  have 
  come 
  

   from 
  far. 
  No 
  agglomerates 
  like 
  those 
  noticed 
  in 
  the 
  Kawant 
  area 
  were 
  

   met 
  with. 
  But 
  their 
  absence 
  may 
  be 
  attributable 
  to 
  the 
  sub 
  -aerial 
  origin 
  

   of 
  the 
  trap 
  about 
  Mandlesar, 
  and 
  the 
  greater 
  liability 
  of 
  loose 
  heaps 
  of 
  

   scoriae 
  to 
  be 
  destroyed 
  by 
  denudation 
  than 
  stratified 
  beds 
  of 
  the 
  same 
  

   material 
  like 
  the 
  Kawant 
  tuff. 
  

  

  The 
  hills 
  west 
  of 
  Barwani 
  (outlying 
  spurs 
  of 
  the 
  Satpura 
  range) 
  exhi- 
  

   bit 
  a 
  number 
  of 
  dykes 
  running 
  in 
  an 
  east-west 
  direction. 
  The 
  number 
  

   and 
  extent 
  of 
  these 
  could 
  not 
  be 
  ascertained, 
  as 
  the 
  district 
  was 
  very 
  

   cursorily 
  examined. 
  Several 
  were 
  noticed 
  near 
  the 
  ancient 
  fort 
  of 
  Rajgarh 
  

   by 
  the 
  Goi 
  river. 
  These 
  were 
  found 
  to 
  be 
  composed 
  of 
  two 
  widely 
  

   different 
  kinds 
  of 
  rock, 
  one 
  basic 
  crystalline 
  like 
  the 
  dyke 
  rock 
  at 
  Mand- 
  

   lesar, 
  the 
  other 
  a 
  singular 
  felspathic 
  rock. 
  The 
  latter 
  is 
  very 
  hard, 
  

   harder 
  than 
  the 
  trap 
  of 
  the 
  neighbourhood, 
  and. 
  in 
  consequence 
  invari- 
  

   ably 
  forms 
  the 
  summits 
  of 
  ridges, 
  being 
  thus 
  visible 
  from 
  far. 
  It 
  con- 
  

   sists 
  of 
  small, 
  whitish, 
  irregular 
  crystals 
  of 
  decomposed 
  felspar 
  (ortho- 
  

   clastic) 
  interspersed 
  in 
  a 
  brownish 
  amorphous 
  base. 
  The 
  rock 
  appears 
  to 
  

   be 
  a 
  felstone. 
  1 
  

  

  1 
  These 
  dykes 
  are 
  alluded 
  to 
  by 
  Mr. 
  Blanford 
  as 
  "peculiar 
  brecciated 
  veins." 
  He 
  

   attributes 
  them 
  to 
  small 
  faults. 
  (Mem. 
  VI, 
  pt. 
  3, 
  pp. 
  106 
  and 
  107.) 
  

  

  ( 
  56 
  ) 
  

  

  