﻿GABBRO 
  OP 
  CARROCK 
  FELL 
  IN 
  THE 
  LAKE 
  DISTRICT. 
  303 
  

  

  rocks 
  are 
  the 
  occurrence 
  of 
  minute 
  granules 
  and 
  crystals 
  of 
  augite, 
  

   of 
  porphyritic 
  crystals 
  of 
  felspar, 
  augite, 
  &c, 
  and 
  of 
  felspar 
  spheru- 
  

   lites. 
  The 
  tendency 
  of 
  the 
  iron-ore 
  to 
  collect 
  round 
  the 
  skeleton 
  - 
  

   forms 
  is 
  well 
  marked 
  in 
  the 
  diabase-porphyrites. 
  In 
  the 
  glassy 
  

   character 
  of 
  the 
  vein 
  the 
  Carrock-Fell 
  rock 
  resembles 
  some 
  of 
  the 
  

   glassy 
  forms 
  of 
  augite-porphyrite 
  and 
  some 
  basalt-glasses. 
  

  

  But 
  the 
  rock 
  to 
  which 
  the 
  Carrock-Fell 
  tachylyte 
  most 
  nearly 
  

   approaches 
  appears 
  to 
  be 
  the 
  typical 
  variolite 
  of 
  Durance 
  *. 
  It 
  

   agrees 
  with 
  this 
  rock 
  in 
  the 
  presence, 
  nature, 
  and 
  behaviour 
  of 
  the 
  

   varioles 
  (spherulites), 
  in 
  the 
  nature 
  of 
  the 
  pyroxene-granules, 
  and 
  

   in 
  the 
  presence 
  of 
  a 
  green 
  ground-mass. 
  An 
  important 
  difference, 
  

   however, 
  from 
  this 
  type 
  is 
  the 
  glassy 
  condition 
  of 
  the 
  ground-mass. 
  

   This, 
  in 
  all 
  typical 
  variolites, 
  is 
  not 
  isotropic, 
  but 
  contains 
  numerous 
  

   minute 
  particles 
  of 
  chlorite, 
  often 
  associated 
  with 
  actinolite 
  and 
  

   epidote. 
  These 
  Eosenbusch 
  holds 
  to 
  be 
  of 
  secondary 
  origin, 
  and 
  Mr. 
  

   Cole 
  has 
  lately 
  suggested 
  that 
  variolites 
  are 
  altered 
  tachylytes 
  f 
  . 
  

   The 
  Carrock-Fell 
  tachylyte 
  seems 
  to 
  support 
  these 
  conclusions, 
  the 
  

   primitive 
  glassy 
  condition 
  having 
  been 
  to 
  a 
  large 
  extent 
  preserved. 
  

  

  There 
  are, 
  however, 
  other 
  points 
  of 
  difference 
  which 
  are 
  original. 
  

   Of 
  these 
  we 
  may 
  mention 
  the 
  frequent 
  association 
  of 
  the 
  variolites 
  

   with 
  magnetite, 
  which 
  often 
  renders 
  them 
  more 
  opaque 
  than 
  the 
  

   surrounding 
  ground-mass 
  ; 
  the 
  occurrence 
  of 
  well- 
  developed 
  por- 
  

   phyritic 
  crystals 
  of 
  plagioelase, 
  augite, 
  and 
  quartz, 
  and 
  of 
  quartz- 
  

   spherules 
  in 
  the 
  ground-mass 
  ; 
  the 
  mode 
  of 
  occurrence 
  of 
  the 
  rock 
  ; 
  

   and 
  its 
  association 
  with 
  a 
  quartz-bearing 
  gabbro. 
  

  

  The 
  Carrock-Fell 
  rock 
  is 
  thus 
  referable 
  to 
  none 
  of 
  the 
  species 
  of 
  

   tachylyte 
  hitherto 
  described, 
  and 
  may 
  perhaps 
  be 
  regarded 
  as 
  a 
  

   quartz-gabbro-vitrophyrite. 
  

  

  Conclusions. 
  

  

  The 
  Carrock-Fell 
  tachylyte 
  is 
  a 
  basic 
  glassy 
  rock 
  associated 
  with 
  

   a 
  quartz-gabbro, 
  and 
  consisting 
  of 
  a 
  well-preserved, 
  globulitic, 
  and 
  

   crystallitic 
  glass-basis 
  containing 
  spherical 
  granules 
  of 
  quartz, 
  sphe- 
  

   rulitic 
  felspars, 
  and 
  a 
  series 
  of 
  pyroxene-granules 
  and 
  granular 
  

   aggregates, 
  which 
  likewise 
  frequently 
  assume 
  a 
  spherulitic 
  form. 
  

   It 
  is 
  rendered 
  micro-porphyritic 
  by 
  the 
  sparing 
  development 
  of 
  

   crystals 
  (or 
  skeleton-crystals) 
  of 
  quartz, 
  felspar, 
  and 
  augite. 
  Owing 
  

   to 
  the 
  mode 
  of 
  development 
  and 
  to 
  the 
  variety 
  of 
  its 
  constituents 
  it 
  

   possesses 
  a 
  very 
  complicated 
  structure. 
  It 
  shows 
  resemblances 
  to 
  

   the 
  glassy 
  forms 
  (variolites) 
  associated 
  with 
  euphotide, 
  and 
  to 
  those 
  

   associated 
  with 
  less 
  deeply 
  seated 
  basic 
  rocks. 
  

  

  In 
  conclusion, 
  I 
  must 
  express 
  my 
  best 
  thanks 
  to 
  Messrs. 
  Hill 
  and 
  

   Bonney 
  for 
  the 
  loan 
  of 
  specimens 
  and 
  slides 
  of 
  variolite, 
  to 
  Messrs. 
  

   Judd, 
  Cole, 
  and 
  Davies 
  for 
  opportunities 
  of 
  examining 
  specimens 
  of 
  

   variolite 
  in 
  their 
  museums, 
  and 
  to 
  Mr. 
  Harker 
  for 
  several 
  useful 
  

   suggestions 
  as 
  to 
  the 
  mode 
  of 
  investigating 
  the 
  rock. 
  

  

  * 
  Rosenbusch, 
  op. 
  cit. 
  p. 
  227. 
  

  

  t 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliv. 
  p. 
  307. 
  

  

  Q.J.G.S. 
  No. 
  178. 
  z 
  

  

  