﻿1875.] 
  

  

  supposed 
  Changes 
  in 
  Basaltic 
  Veins. 
  

  

  547 
  

  

  something 
  under 
  this 
  in 
  the 
  other 
  case. 
  These 
  coatings 
  exhibit 
  a 
  marked 
  

   similarity 
  to 
  each 
  other 
  ; 
  but 
  a 
  striking 
  difference 
  in 
  some 
  respects 
  is 
  

   observed 
  to 
  the 
  interior 
  of 
  the 
  mass 
  they 
  surround, 
  

  

  Upper 
  surface. 
  Lower 
  surface. 
  

  

  Silica 
  43-22 
  40-62 
  

  

  Alumina 
  17*44 
  18-18 
  

  

  Protoxide 
  of 
  iron 
  13-03 
  14-00 
  

  

  Sulphide 
  of 
  iron 
  1-31 
  

  

  Lime 
  6-26 
  4-37 
  

  

  Magnesia 
  2-86 
  3-94 
  

  

  Potash 
  1 
  1 
  28 
  ' 
  78 
  

  

  Soda 
  J 
  ~ 
  -33 
  

  

  Carbonic 
  acid 
  14-72 
  13-23 
  

  

  Water 
  1-46 
  2-36 
  

  

  100-27 
  99-12 
  

   In 
  colour 
  these 
  coatings 
  are 
  of 
  a 
  light 
  buff, 
  and 
  are 
  close 
  in 
  texture, 
  in 
  both 
  

   of 
  which 
  particulars 
  they 
  differ 
  considerably 
  from 
  the 
  unchanged 
  basalt. 
  

   It 
  would 
  appear 
  that 
  any 
  difference 
  in 
  composition 
  between 
  the 
  interior 
  

   of 
  this 
  horizontal 
  bed 
  of 
  basalt 
  and 
  its 
  outer 
  surfaces 
  is 
  entirely 
  inde- 
  

   pendent 
  of 
  that 
  which 
  might 
  be 
  supposed 
  to 
  arise 
  from 
  mere 
  contact 
  with 
  

   the 
  adjoining 
  strata. 
  Lying 
  above 
  it 
  is 
  8 
  feet 
  of 
  a 
  siliceous 
  rock 
  known 
  

   among 
  miners 
  in 
  the 
  North 
  of 
  England 
  as 
  a 
  " 
  white 
  post." 
  It 
  was 
  

  

  found 
  to 
  consist 
  of 
  : 
  — 
  

  

  Silica 
  88-25 
  

  

  Alumina 
  5*69 
  

  

  Peroxide 
  of 
  iron 
  1*71 
  

  

  Lime 
  1*53 
  

  

  Magnesia 
  *69 
  

  

  Potash 
  -80 
  

  

  Soda 
  -21 
  

  

  Water 
  1-75 
  

  

  100-63 
  

  

  The 
  underside 
  of 
  the 
  basalt 
  rests 
  upon 
  a 
  thin 
  seam 
  of 
  coal, 
  greatly 
  charred 
  

   by 
  its 
  proximity 
  to 
  so 
  large 
  a 
  volume 
  of 
  matter, 
  which 
  must 
  have 
  arrived 
  at 
  

   its 
  present 
  position 
  in 
  a 
  state 
  of 
  intense 
  heat. 
  This 
  coal 
  is 
  of 
  course 
  defi- 
  

   cient 
  in 
  volatile 
  constituents, 
  and 
  contains 
  a 
  large 
  percentage 
  of 
  ash, 
  one 
  

   half 
  of 
  which 
  is 
  carbonate 
  of 
  lime. 
  Its 
  composition 
  is 
  as 
  follows 
  : 
  — 
  

  

  Carbon 
  56-58 
  

  

  Hydrogen 
  1*00 
  

  

  Oxygen 
  3-52 
  

  

  Sulphur 
  -18 
  

  

  Ash 
  38-65 
  

  

  99-93 
  

  

  