﻿LATERITIC 
  ROCKS. 
  33 
  

  

  Some 
  of 
  these 
  basaltic 
  dykes, 
  having 
  resisted 
  the 
  denuding 
  agencies 
  

   more 
  effectually 
  than 
  the 
  neighbouring 
  rocks, 
  stand 
  up 
  like 
  the 
  ruins 
  

   of 
  a 
  great 
  boundary 
  wall 
  across 
  the 
  country 
  : 
  a 
  fine 
  example 
  may 
  be 
  

   seen 
  just 
  within 
  the 
  hilly 
  ground 
  4| 
  miles 
  south-west 
  of 
  Chotila. 
  

  

  No 
  system 
  as 
  to 
  the 
  bearing 
  of 
  the 
  dykes 
  in 
  the 
  Jurassic 
  area 
  could 
  

   be 
  traced, 
  for 
  they 
  trend 
  in 
  all 
  directions. 
  1 
  

  

  There 
  is, 
  about 
  a 
  mile 
  and 
  a 
  half 
  north 
  of 
  Chotila, 
  a 
  small 
  group 
  of 
  

   Intrusions 
  north 
  of 
  irregular 
  intrusions 
  of 
  fine-grained 
  compact 
  blue- 
  

   Cnotlla 
  - 
  black 
  basalt. 
  That 
  these 
  are 
  actually 
  intrusions, 
  

  

  and 
  not 
  remnants 
  of 
  a 
  trap 
  flow, 
  is 
  shown 
  by 
  the 
  altered 
  indurated 
  state 
  

   of 
  the 
  adjoining 
  sandstone; 
  and 
  further 
  evidence 
  is 
  afforded 
  in 
  the 
  

   frequent 
  occurrence 
  of 
  slickensides 
  here, 
  caused 
  by 
  the 
  pressure 
  of 
  the 
  

   out-flow. 
  

  

  Numerous 
  large 
  dykes 
  are 
  shown 
  on 
  the 
  map 
  in 
  the 
  south-eastern 
  

  

  Dykes 
  numerous 
  in 
  P 
  ar 
  ^ 
  °^ 
  the 
  tra 
  P 
  area 
  ; 
  m 
  the 
  vicinity 
  of 
  Dedan, 
  

   south-eastern 
  area. 
  an( 
  j 
  thence 
  north-eastward 
  as 
  far 
  as 
  Talaja. 
  The 
  

  

  hill 
  ridges, 
  formed 
  by 
  these 
  dykes, 
  have 
  been 
  so 
  clearly 
  delineated 
  by 
  

   the 
  Topographical* 
  Survey, 
  on 
  their 
  large-scale 
  map, 
  that 
  I 
  have 
  not 
  

   hesitated 
  to 
  colour 
  the 
  dykes 
  on 
  them, 
  as 
  time 
  could 
  not 
  be 
  spared 
  to 
  

   traverse 
  the 
  whole 
  area. 
  It 
  will 
  be 
  seen 
  that 
  the 
  general 
  bearing 
  of 
  the 
  

   dykes 
  in 
  this 
  part 
  of 
  the 
  field 
  is 
  west-40°-south 
  to 
  south-west. 
  A 
  few 
  

   cross 
  nearly 
  at 
  right 
  angles. 
  In 
  the 
  north-eastern 
  part 
  the 
  bearings 
  are 
  

   less 
  regular. 
  2 
  

  

  Lateritic 
  rocks. 
  — 
  This 
  group, 
  in 
  the 
  southern 
  and 
  south-eastern 
  divi- 
  

   sions 
  of 
  the 
  province, 
  is 
  only 
  exposed 
  in 
  a 
  few 
  

   Distribution. 
  . 
  

  

  places 
  along 
  the 
  margin 
  or 
  the 
  trap 
  area 
  ; 
  notably, 
  

  

  1 
  It 
  was 
  observed 
  that 
  the 
  agriculturists 
  persistently 
  sink 
  their 
  irrigation 
  wells 
  along 
  

   the 
  dykes, 
  tracing 
  out 
  their 
  course 
  with 
  great 
  assiduity; 
  they 
  are 
  almost 
  invariably 
  re- 
  

   warded 
  by 
  the 
  wells 
  yielding 
  water 
  at 
  a 
  depth 
  within 
  15 
  to 
  20 
  feet 
  of 
  the 
  surface. 
  In 
  

   some 
  instances 
  it 
  would 
  appear 
  that 
  the 
  joints 
  and 
  cracks 
  in 
  the 
  dyke-i*ock 
  communicate 
  

   with 
  some 
  deep-seated 
  water-bed; 
  in 
  other 
  cases 
  the 
  dykes 
  seem 
  to 
  wall 
  up, 
  and 
  keep 
  in 
  on 
  

   one 
  side, 
  the 
  water 
  of 
  the 
  adjoiuing 
  strata. 
  

  

  2 
  The 
  map 
  published 
  with 
  this 
  memoir 
  is 
  on 
  so 
  small 
  a 
  scale, 
  that 
  only 
  a 
  limited 
  number 
  

   of 
  the 
  dykes 
  can 
  be 
  shown 
  ; 
  very 
  many 
  more 
  have 
  been 
  recorded 
  on 
  the 
  large 
  field-map 
  in 
  

   the 
  Geological 
  burvey 
  Office. 
  

  

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