﻿28 
  F00TE 
  : 
  GEOLOGY 
  OF 
  MADRAS. 
  

  

  be 
  considered. 
  The 
  several 
  patches 
  in 
  which 
  the 
  laterite 
  there 
  occurs 
  

   are 
  manifestly 
  but 
  the 
  remains 
  of 
  one 
  continuous 
  formation 
  cut 
  across 
  

   by 
  the 
  eroding 
  action 
  of 
  the 
  larger 
  rivers 
  as 
  the 
  land 
  was 
  gradually 
  

   rising 
  above 
  the 
  sea. 
  The 
  parallelism 
  of 
  this 
  band 
  of 
  laterite 
  with 
  the 
  

   coast 
  on 
  one 
  side, 
  and 
  with 
  the 
  general 
  strike 
  of 
  the 
  high 
  ground 
  of 
  the 
  

   peninsula 
  on 
  the 
  other, 
  is 
  most 
  marked. 
  

  

  To 
  suppose 
  this 
  laterite 
  to 
  have 
  been 
  deposited 
  in 
  a 
  fresh-water 
  or 
  

   brackish 
  lagoon 
  involves 
  the 
  conception 
  of 
  a 
  barrier 
  of 
  extraordinary 
  

   length 
  and 
  breadth 
  to 
  be 
  sufficient 
  to 
  exclude 
  the 
  sea 
  and 
  to 
  retain 
  the 
  

   waters 
  brought 
  down 
  by 
  numerous 
  rivers 
  along 
  a 
  line 
  several 
  hundred 
  miles 
  

   in 
  length. 
  Moreover, 
  the 
  fresh 
  and 
  brackish 
  water 
  deposits 
  which 
  have 
  

   been 
  formed 
  in 
  the 
  lagoons 
  now 
  existing 
  in 
  no 
  way 
  resemble 
  the 
  lateritic 
  

   formations. 
  

  

  The 
  typical 
  laterite 
  of 
  Buchanan 
  may 
  be 
  described 
  as 
  an 
  impure 
  

  

  Its 
  lithological 
  charac 
  red 
  sand 
  F 
  cla 
  y> 
  as 
  a 
  mle 
  vei 
  T 
  lar 
  g 
  el 
  F 
  impregnated 
  

   ters- 
  with 
  iron 
  in 
  the 
  form 
  of 
  brown 
  hsematite, 
  and 
  

  

  remarkable 
  for 
  its 
  tendency 
  to 
  form 
  concretionary 
  conglomeratic 
  masses, 
  

   abounding 
  in 
  vesicular 
  and 
  vermicular 
  cavities, 
  which 
  are 
  generally 
  

   filled 
  with 
  a 
  lighter- 
  colored 
  soft 
  lithomargic 
  clay. 
  When 
  freshly 
  

   quarried 
  the 
  mass 
  is 
  often 
  soft 
  enough 
  to 
  be 
  cut 
  with 
  an 
  axe 
  or 
  spade 
  

   and 
  trimmed 
  into 
  shapes 
  convenient 
  for 
  building 
  purposes 
  ; 
  but 
  under 
  

   atmospheric 
  influences 
  it 
  soon 
  hardens, 
  and 
  after 
  a 
  time 
  becomes 
  coated 
  

   with 
  a 
  hard 
  ferruginous 
  glaze. 
  The 
  softer 
  clay 
  occupying 
  the 
  vermicu- 
  

   lar 
  cavities 
  communicating 
  with 
  the 
  surface 
  will 
  then 
  generally 
  be 
  

   found 
  to 
  have 
  been 
  washed 
  out, 
  giving 
  the 
  surface 
  of 
  the 
  rock 
  a 
  very 
  

   rough 
  porous 
  appearance. 
  It 
  is 
  this 
  scabrous 
  looking 
  rock 
  to 
  which 
  the 
  

   Tamil 
  people 
  have 
  given 
  the 
  name 
  of 
  ' 
  shuri 
  kal' 
  or 
  'itch-stone/ 
  

  

  In 
  many 
  parts 
  of 
  the 
  Peninsula 
  this 
  rock 
  is 
  largely 
  quarried 
  for 
  

   building 
  purposes 
  and 
  forms 
  a 
  substitute 
  for 
  bricks, 
  — 
  a 
  use 
  which 
  appears 
  

   to 
  have 
  suggested 
  the 
  name 
  to 
  Dr. 
  Buchanan, 
  who 
  adopted 
  the 
  latin 
  

   word 
  e 
  later' 
  a 
  brick, 
  as 
  the 
  root 
  for 
  the 
  new 
  name 
  he 
  coined. 
  

  

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