﻿I 
  292 
  ] 
  

   XXXIV. 
  Proceedings 
  of 
  Learned 
  Societies. 
  

  

  GEOLOGICAL 
  SOCIETY. 
  

  

  [Continued 
  from 
  p. 
  140.] 
  

  

  November 
  21st, 
  1917.— 
  Dr. 
  Alfred 
  Harker, 
  E.K.S., 
  President, 
  

   in 
  the 
  Chair. 
  

  

  HHHE 
  following 
  communication 
  was 
  read 
  : 
  — 
  

  

  ' 
  The 
  Shap 
  Minor 
  Intrusions.' 
  By 
  James 
  Morrison, 
  B.A., 
  B.Sc. 
  

  

  The 
  paper 
  deals 
  with 
  the 
  minor 
  igneous 
  intrusions 
  occurring 
  in 
  

   the 
  triangular 
  area 
  between 
  Shap, 
  Windermere, 
  and 
  Sedbergh. 
  

  

  From 
  their 
  field 
  relations 
  and 
  petrographic 
  characters 
  the 
  in- 
  

   trusions 
  are 
  found 
  to 
  belong 
  to 
  one 
  or 
  the 
  other 
  of 
  two 
  well-marked 
  

   groups, 
  a 
  division 
  which 
  is 
  regarded 
  as 
  connoting 
  also 
  an 
  age- 
  

   classification. 
  

  

  The 
  rocks 
  of 
  the 
  earlier 
  set, 
  characterized 
  by 
  the 
  presence 
  of 
  large 
  

   orthoclase-felspars 
  of 
  the 
  granitic 
  type, 
  are 
  intimately 
  associated 
  

   with 
  the 
  granite, 
  to 
  the 
  immediate 
  neighbourhood 
  of 
  which 
  they 
  

   are 
  practically 
  confined. 
  The 
  rocks 
  range 
  from 
  quartz-felsites 
  to 
  

   lamprophyres. 
  Of 
  considerable 
  interest 
  in 
  this 
  group 
  is 
  a 
  series 
  of 
  

   hybrid 
  intrusions, 
  consisting 
  essentially 
  of 
  rocks 
  of 
  a 
  more 
  or 
  less 
  

   basic 
  magma 
  enclosing 
  xenocrysts 
  of 
  a 
  more 
  acid 
  (but 
  allied) 
  

   magma 
  obtained 
  by 
  settlement 
  under 
  intratelluric 
  conditions. 
  The 
  

   constitution 
  of 
  any 
  given 
  member 
  of 
  the 
  series 
  is 
  determined 
  by 
  

   two 
  factors 
  : 
  the 
  abundance 
  of 
  xenocrysts 
  and 
  the 
  composition 
  of 
  the 
  

   matrix, 
  an 
  increasing 
  basicity 
  in 
  the 
  latter 
  (due 
  to 
  original 
  magma 
  tic 
  

   differentiation) 
  and 
  a 
  decrease 
  in 
  the 
  former 
  marking 
  the 
  successive 
  

   stages. 
  The 
  more 
  acid 
  have 
  affinities 
  with 
  the 
  porphyrites, 
  the 
  

   more 
  basic 
  with 
  the 
  lamprophyres, 
  the 
  series 
  ranging 
  from 
  modified 
  

   biotite-porphyrites 
  to 
  modified 
  pilitic 
  lamprophyres. 
  

  

  The 
  later 
  intrusions 
  are 
  typically 
  free 
  from 
  the 
  large 
  orthoclase- 
  

   felspars, 
  though 
  quartz-grains 
  may 
  occur 
  even 
  in 
  the 
  basic 
  members. 
  

   Associated 
  centrally 
  with 
  the 
  earlier 
  set 
  they 
  are 
  distributed 
  over 
  

   a 
  much 
  wider 
  area, 
  overlapping 
  the 
  former 
  in 
  every 
  direction. 
  They 
  

   are 
  the 
  result 
  of 
  a 
  further 
  differentiation, 
  and 
  are 
  assigned 
  to 
  a 
  

   later 
  period 
  when 
  igneous 
  activity 
  was 
  renewed 
  on 
  a 
  more 
  or 
  less 
  

   regional 
  scale. 
  The 
  rocks 
  include 
  acid 
  felsites 
  and 
  spessartites. 
  

  

  The 
  rocks 
  of 
  the 
  earlier 
  set 
  agree 
  in 
  general 
  direction 
  with 
  the 
  

   north-north-west 
  fractures 
  transverse 
  to 
  the 
  strike 
  of 
  the 
  country- 
  

   rock, 
  while 
  the 
  later 
  intrusions 
  trend 
  generally 
  east 
  of 
  north. 
  

  

  