﻿6 
  FOOTE 
  : 
  GEOLOGY 
  OF 
  MADRAS. 
  

  

  The 
  next 
  writer 
  in 
  point 
  of 
  time 
  was 
  Dr. 
  Benza, 
  of 
  the 
  Madras 
  

  

  Medical 
  Service. 
  In 
  a 
  paper 
  he 
  published 
  in 
  the 
  

   Dr. 
  Benza. 
  

  

  Madras 
  Journal 
  of 
  Literature 
  and 
  Science 
  for 
  

   July 
  1836, 
  Dr. 
  Benza 
  remarks 
  that 
  ' 
  granite'' 
  is 
  the 
  lowest 
  rock 
  iu 
  the 
  

   Madras 
  plain, 
  and 
  occurs 
  intermixed 
  with 
  pegmatite 
  at 
  the 
  Marmalong 
  

   bridge, 
  and 
  on 
  the 
  Guiudy 
  race 
  course. 
  By 
  granite, 
  Dr. 
  Benza 
  must 
  

   have 
  meant 
  the 
  more 
  compact 
  beds 
  of 
  hornblendic 
  aud 
  felspathic 
  

   gneiss. 
  He 
  further 
  notices 
  the 
  occurrence 
  of 
  garnetiferous 
  gneiss 
  at 
  

   Palaveram, 
  also 
  the 
  formation 
  of 
  Kaolin 
  by 
  the 
  decomposition 
  of 
  the 
  

   pegmatite. 
  The 
  hornblende 
  slate 
  and 
  rock* 
  at 
  St. 
  Thomas' 
  Mount 
  

   and 
  Palaveram 
  are 
  stated 
  to 
  be 
  overlying 
  the 
  fundamental 
  granite. 
  

   Borings 
  for 
  water 
  near 
  Madras, 
  Dr. 
  Benza 
  justly 
  considers 
  unlikely 
  

   to 
  be 
  successful. 
  

  

  With 
  reference 
  to 
  laterite 
  he 
  remarks 
  that 
  conglomeratic 
  laterite, 
  

   either 
  undisintegrated 
  or 
  detrital, 
  extends 
  nearly 
  over 
  the 
  whole 
  plains. 
  

   He 
  further 
  points 
  out 
  the 
  occurrence 
  of 
  the 
  detrital 
  laterite 
  in 
  two 
  

   geological 
  positions, 
  Istly, 
  as 
  loose, 
  round 
  pebbles 
  scattered 
  all 
  over 
  the 
  

   surface 
  ; 
  %ndly> 
  as 
  a 
  substratum 
  to 
  the 
  soil 
  often 
  many 
  feet 
  thick, 
  

   with 
  undecomposed 
  pieces 
  of 
  compact 
  conglomerate 
  ; 
  the 
  detritus 
  being 
  

   derived 
  from 
  the 
  present 
  conglomerate. 
  

  

  He 
  mentions 
  the 
  occurrence 
  of 
  dykes 
  of 
  ' 
  basaltic 
  hornblende' 
  

   trap 
  between 
  Palaveram 
  and 
  Trimatoor. 
  

  

  The 
  occurrence 
  of 
  ' 
  marine 
  organic 
  exuvia?' 
  in 
  the 
  clayey 
  stratum 
  

   underlying 
  the 
  Madras 
  sands 
  is 
  also 
  recorded 
  by 
  Dr. 
  Benza, 
  whose 
  

   remarks, 
  though 
  very 
  brief, 
  are 
  generally 
  judicious, 
  and 
  show 
  that 
  he 
  

   was 
  a 
  good 
  observer. 
  

  

  In 
  the 
  same 
  number 
  of 
  the 
  Madras 
  Journal 
  (July, 
  1836), 
  with 
  

  

  Dr. 
  Benza's 
  paper 
  appeared 
  a 
  valuable 
  Memoir 
  

   Mr. 
  Robert 
  Cole. 
  

  

  " 
  On 
  the 
  geological 
  position 
  and 
  association 
  of 
  the 
  

  

  laterite 
  or 
  iron 
  clay 
  formation 
  of 
  India 
  with 
  a 
  description 
  of 
  that 
  rock 
  

  

  * 
  The 
  ' 
  hornblende 
  rock' 
  i- 
  merely 
  ;i 
  verj 
  compact 
  variety 
  of 
  liorubleudic 
  gneiss. 
  

   ( 
  6 
  ) 
  . 
  

  

  