﻿410 
  MR. 
  T. 
  H. 
  HOLLAND 
  ON 
  ATJGITE-DIORITES 
  WITH 
  [Allg. 
  1 
  897, 
  

  

  augite 
  and 
  plagioclase 
  show 
  that 
  these 
  two 
  constituents 
  consolidated 
  

   approximately 
  simultaneously, 
  while 
  there 
  is 
  no 
  doubt 
  that 
  tho 
  

   micropegmatite 
  was 
  formed 
  subsequently. 
  The 
  principal 
  question 
  

   to 
  decide 
  is 
  whether 
  the 
  micropegmatite 
  was 
  formed 
  — 
  

  

  (a) 
  During 
  the 
  primary 
  consolidation 
  of 
  the 
  magma 
  which 
  was 
  

   injected 
  to 
  form 
  the 
  dykes 
  ; 
  

  

  (6) 
  By 
  secondary 
  changes 
  induced 
  in 
  the 
  rock 
  ; 
  or 
  

  

  (c) 
  By 
  subsequent 
  intrusion 
  of 
  granophync 
  material 
  into 
  the 
  

   augite-plagioclase 
  rock. 
  

  

  The 
  complete 
  absence 
  of 
  granitic 
  intrusions, 
  and 
  for 
  that 
  matter 
  

   of 
  intrusions 
  of 
  any 
  sort, 
  into 
  the 
  very 
  large 
  number 
  of 
  basic 
  dykes 
  

   which 
  have 
  been 
  carefully 
  examined 
  in 
  Southern 
  India 
  puts 
  the 
  third 
  

   consideration 
  out 
  of 
  the 
  question. 
  The 
  remarkable 
  freshness 
  of 
  the 
  

   rocks 
  — 
  their 
  escape 
  from 
  crushing 
  movements, 
  as 
  well 
  as 
  their 
  

   freedom 
  from 
  the 
  signs 
  of 
  subaerial 
  hydration 
  — 
  precludes 
  the 
  possi- 
  

   bility 
  of 
  explaining 
  the 
  presence 
  of 
  the 
  micropegmatite 
  as 
  the 
  result 
  

   of 
  secondary 
  changes. 
  But 
  besides 
  the 
  removal 
  of 
  alternative 
  

   explanations 
  by 
  very 
  complete 
  and 
  satisfactory 
  negative 
  evidence 
  

   in 
  so 
  large 
  a 
  number 
  of 
  instances 
  in 
  which 
  these 
  points 
  of 
  evidence 
  

   have 
  been 
  tested, 
  the 
  first 
  explanation 
  offered 
  — 
  -namely, 
  that 
  the 
  

   micropegmatite 
  is 
  primary 
  in 
  origin 
  — 
  is 
  supported 
  uniformly 
  by 
  

  

  (1) 
  The 
  crystallographic 
  continuity 
  of 
  its 
  felspar 
  with 
  that 
  of 
  the 
  

   normal 
  plagioclase 
  of 
  the 
  rock. 
  

  

  (2) 
  Its 
  occurrence 
  filling 
  in 
  the 
  angles 
  and 
  spaces 
  between 
  the 
  

   augite 
  and 
  plagioclase, 
  thus 
  playing 
  the 
  part 
  of 
  groundmass 
  ; 
  and 
  

  

  (3) 
  Its 
  variation 
  in 
  coarseness 
  of 
  grain 
  agreeing 
  with 
  that 
  of 
  the 
  

   remaining 
  two 
  constituents 
  of 
  the 
  rock. 
  In 
  the 
  centres 
  of 
  the 
  

   large 
  dykes 
  the 
  separation 
  of 
  the 
  quartz 
  from 
  felspar 
  in 
  the 
  micro- 
  

   pegmatitic 
  patches 
  can 
  easily 
  be 
  seen 
  with 
  low 
  powers 
  ; 
  in 
  the 
  fine- 
  

   grained 
  portions 
  nearer 
  the 
  margins, 
  and 
  in 
  the 
  smaller 
  dykes, 
  the 
  

   intergrowth 
  of 
  these 
  two 
  minerals 
  is 
  on 
  so 
  minute 
  a 
  scale 
  that 
  

   even 
  with 
  high 
  powers 
  their 
  individualization 
  is 
  not 
  evident. 
  

   Had 
  the 
  micropegmatite 
  been 
  introduced 
  into 
  the 
  rock 
  by 
  subsequent 
  

   intrusion, 
  or 
  had 
  it 
  been 
  caused 
  by 
  secondary 
  changes, 
  such 
  a 
  

   relation 
  between 
  its 
  structure 
  and 
  that 
  of 
  the 
  rock 
  would 
  have 
  been 
  

   merely 
  fortuitous, 
  and 
  therefore 
  never 
  an 
  uniform 
  rule. 
  

  

  The 
  formation 
  of 
  the 
  micropegmatite 
  is, 
  therefore, 
  dependent 
  

   directly 
  upon 
  the 
  processes 
  by 
  which 
  consolidation 
  of 
  the 
  magma 
  

   has 
  been 
  accomplished, 
  and 
  represents 
  the 
  final 
  stage 
  of 
  that 
  

   consolidation. 
  

  

  The 
  consolidation 
  of 
  the 
  rock 
  may 
  thus 
  be 
  divided 
  into 
  two 
  

   distinct, 
  though 
  perfectly 
  continuous, 
  processes 
  : 
  — 
  

  

  (1) 
  The 
  crystallization 
  of 
  the 
  augite 
  and 
  plagioclase, 
  which 
  make 
  

   up 
  the 
  principal 
  mass 
  of 
  the 
  rock, 
  to 
  form 
  a 
  strong 
  framework. 
  

  

  (2) 
  The 
  formation 
  of 
  micropegmatite 
  from 
  the 
  residual 
  mother- 
  

   liquor 
  filling 
  the 
  angular 
  spaces 
  and 
  interstices 
  in 
  the 
  framework 
  of 
  

   augite 
  and 
  plagioclase. 
  

  

  As 
  the 
  crystallization 
  of 
  the 
  mother-liquor 
  filling 
  in 
  the 
  inter- 
  

   crystal 
  lacunae 
  and 
  their 
  ramifying 
  connexions 
  would 
  be 
  attended 
  

   with 
  the 
  usual 
  reduction 
  in 
  volume, 
  and 
  as 
  the 
  framework 
  of 
  augite- 
  

  

  