﻿METAMORPHIC 
  ROCKS. 
  129 
  

  

  the 
  bedding'. 
  The 
  difficulty 
  which 
  arises 
  in 
  this 
  case 
  is 
  to 
  decide 
  whe- 
  

   ther 
  it 
  is 
  a 
  highly 
  metamorphosed 
  bed 
  of 
  pure 
  

  

  ^UR.rtz 
  i*oc.Kr 
  

  

  quartzite 
  or 
  a 
  vein 
  of 
  laminated 
  vein 
  quartz, 
  for 
  

   the 
  bedding' 
  seems 
  to 
  coincide 
  in 
  every 
  way 
  with 
  the 
  under 
  and 
  over- 
  

   lying 
  beds 
  of 
  hornblendic 
  gneiss, 
  but 
  on 
  the 
  summit 
  of 
  the 
  hill 
  it 
  

   presents 
  an 
  appearance 
  which 
  might 
  be 
  the 
  result 
  of 
  sudden 
  thinning 
  

   out, 
  but 
  might 
  also 
  be 
  considered 
  as 
  proof 
  of 
  injection 
  along 
  the 
  strike 
  

   of 
  the 
  hornblendic 
  beds 
  which 
  dip 
  75° 
  to 
  80° 
  east 
  by 
  south. 
  

  

  The 
  outlying 
  patches 
  of 
  gneiss 
  which 
  crop 
  out 
  through 
  the 
  sedi- 
  

   mentary 
  formations 
  west 
  of 
  the 
  Chingleput 
  gneiss 
  area 
  have 
  all 
  a 
  more 
  

   or 
  less 
  north-north-east 
  strike, 
  and 
  evidently 
  form 
  parts 
  of 
  the 
  same 
  or 
  

   another 
  great 
  series 
  of 
  foldings. 
  

  

  The 
  gneissic 
  rocks 
  lying 
  west 
  of 
  the 
  old 
  Palar 
  alluvial 
  valley 
  are 
  

  

  almost 
  everywhere 
  very 
  granitoid 
  in 
  character 
  ; 
  

   Granitoid 
  gneiss. 
  

  

  the 
  strike 
  of 
  the 
  beds, 
  which 
  is 
  generally 
  more 
  

  

  southerly 
  than 
  between 
  Madras 
  and 
  Chingleput, 
  very 
  frequently 
  most 
  

   obscure 
  and 
  not 
  seldom 
  quite 
  undeterminable. 
  Like 
  the 
  granitoid 
  

   gneiss 
  of 
  South 
  Arcot, 
  which 
  it 
  frequently 
  resembles 
  in 
  every 
  respect, 
  

   there 
  is 
  a 
  great 
  tendency 
  to 
  weather 
  .into 
  tors 
  and 
  piles 
  of 
  great 
  loose 
  

   blocks. 
  

  

  The 
  rocks 
  are 
  generally 
  very 
  coarse-grained 
  and 
  chiefly 
  quartzo- 
  

   felspathic, 
  and 
  contain 
  but 
  a 
  small 
  proportion 
  of 
  hornblende 
  or 
  more 
  

   rarely 
  of 
  mica. 
  They 
  are 
  more 
  largely 
  felspathic 
  than 
  the 
  non-granitoid 
  

   gneiss. 
  

  

  The 
  granitoid 
  gneiss, 
  like 
  the 
  more 
  typical 
  gneissic 
  beds 
  to 
  the 
  

   east, 
  evidently 
  forms 
  great 
  foldings, 
  but 
  they 
  are 
  less 
  perfect, 
  and, 
  from 
  

   the 
  greater 
  change 
  the 
  rocks 
  have 
  undergone, 
  far 
  more 
  difficult 
  to 
  recog- 
  

   nize. 
  

  

  It 
  is 
  from 
  the 
  decay 
  of 
  similar 
  highly 
  felspathic 
  coarse 
  granitoid 
  

  

  gneiss 
  rocks, 
  which 
  occur 
  very 
  extensively 
  on 
  the 
  east 
  side 
  of 
  the 
  

   r 
  ( 
  129 
  ) 
  

  

  