﻿1864.] 
  MURCHISON 
  AND 
  HARKNESS 
  PERMIAN. 
  161 
  

  

  iron 
  is 
  in 
  smaller 
  proportions 
  ; 
  and 
  in 
  this 
  white 
  sandstone 
  there 
  is 
  

   no 
  incrusting 
  oxide 
  of 
  iron. 
  The 
  presence 
  of 
  oxide 
  of 
  iron 
  as 
  an 
  

   incrusting 
  material 
  at 
  this 
  early 
  period 
  of 
  the 
  Permian 
  formation 
  is 
  

   a 
  proof 
  of 
  the 
  abundance 
  of 
  the 
  substance, 
  which 
  now 
  occurs 
  as 
  

   veins 
  of 
  haematite 
  filling 
  up 
  the 
  fissures 
  in 
  the 
  Carboniferous 
  rocks, 
  

   during 
  the 
  commencement 
  of 
  the 
  Permian 
  epoch. 
  

  

  The 
  presence 
  of 
  silicate 
  of 
  magnesia 
  as 
  a 
  cementing 
  material 
  in 
  

   the 
  quartz-granules 
  in 
  the 
  Penrith 
  sandstones 
  indicates 
  the 
  early 
  

   occurrence 
  of 
  magnesia, 
  a 
  substance 
  more 
  abundant 
  in 
  the 
  Permian 
  

   than 
  in 
  any 
  other 
  group 
  of 
  rocks. 
  

  

  Evidence 
  of 
  the 
  occurrence 
  of 
  abundance 
  of 
  magnesia 
  during 
  the 
  

   Permian 
  epoch 
  becomes 
  more 
  prominent 
  in 
  the 
  upper 
  beds 
  of 
  the 
  

   Penrith 
  sandstones, 
  a 
  portion 
  of 
  dolomitized 
  Carboniferous 
  Limestone 
  

   from 
  the 
  magnesian 
  breccias 
  of 
  Hilton-beck 
  yielding 
  Dr. 
  Blyth 
  the 
  

   following 
  results 
  : 
  — 
  

  

  CaO,C0 
  2 
  650 
  

  

  MgO, 
  C0 
  2 
  29-4 
  

  

  Carbonate 
  of 
  iron 
  and 
  silica 
  . 
  . 
  5-6 
  

  

  lOCK) 
  

  

  Eegarding 
  this 
  rock 
  Dr. 
  Blyth 
  observes 
  that, 
  by 
  deducting 
  the 
  

   carbonate 
  of 
  iron 
  and 
  silica, 
  and 
  calculating 
  the 
  mixed 
  carbonates 
  of 
  

   lime 
  and 
  magnesia, 
  we 
  have 
  

  

  CaO, 
  C0 
  2 
  68-8 
  

  

  MgO,C0 
  2 
  31-2 
  

  

  100-0 
  

   Pammelsberg 
  has 
  given 
  three 
  proportions, 
  to 
  which 
  the 
  composi- 
  

   tion 
  of 
  bitter 
  spar 
  and 
  dolomite 
  approximates 
  more 
  or 
  less 
  (Bischof, 
  

   ii. 
  p. 
  47), 
  namely 
  : 
  — 
  

  

  First, 
  ICaO, 
  C0 
  2 
  54-18 
  

  

  lMgO,C0 
  2 
  45-82 
  

  

  100-00 
  

  

  Second, 
  3CaO,C0 
  2 
  63-95 
  

  

  2MgO,C0 
  3 
  36-05 
  

  

  100-00 
  

  

  Third, 
  2CaO,C0 
  2 
  70-28 
  

  

  lMgO,C0 
  2 
  29-72 
  

  

  100-00 
  

  

  The 
  dolomite 
  of 
  the 
  magnesian 
  breccia 
  of 
  Hilton-beck 
  agrees 
  

   nearly 
  with 
  the 
  third 
  approximate 
  formula 
  which 
  Hammelsberg 
  gives 
  

   for 
  dolomite 
  =2 
  CaO, 
  C0 
  2 
  + 
  MgO, 
  C0 
  2 
  . 
  Of 
  this 
  composition 
  are 
  the 
  

   dolomites 
  from 
  Kolozomek, 
  of 
  Gliicksbrunn 
  *, 
  and 
  a 
  variety 
  from 
  the 
  

   Tillerthal. 
  The 
  dolomitizing 
  here 
  has 
  been 
  complete. 
  

  

  Reference 
  has 
  already 
  been 
  made 
  to 
  the 
  hard 
  veins 
  of 
  light- 
  

   coloured 
  sandstone 
  which 
  intersect 
  the 
  lower 
  sandstones. 
  Their 
  

  

  * 
  For 
  a 
  description 
  of 
  the 
  dolomites 
  of 
  Gliicksbrunn, 
  and 
  their 
  position, 
  see 
  

   • 
  Siluria,' 
  2nd 
  edit. 
  p. 
  340. 
  

  

  VOL. 
  XX. 
  — 
  PART 
  I. 
  M 
  

  

  