﻿418 
  ME. 
  T. 
  H. 
  HOLLAND 
  ON 
  ATJGITE- 
  DI0EITES 
  WITH 
  [Aug. 
  1897, 
  

  

  Prof. 
  G. 
  A. 
  J. 
  Cole 
  observed 
  that, 
  while 
  the 
  dyke-like 
  and 
  sheet- 
  

   like 
  masses 
  of 
  Madras 
  and 
  the 
  "Whin 
  Sill 
  of 
  England, 
  taken 
  alone, 
  

   would 
  certainly 
  seem 
  to 
  support 
  the 
  view 
  of 
  differentiation 
  of 
  one 
  

   original 
  magma, 
  yet 
  the 
  matter 
  mnst 
  be 
  judged 
  by 
  comparison 
  with 
  

   areas 
  which 
  the 
  Author 
  has 
  himself 
  quoted. 
  The 
  speaker 
  had 
  

   recently 
  returned 
  from 
  Siieve 
  Gallion, 
  in 
  South-eastern 
  Londonderry, 
  

   where 
  a 
  granite, 
  probably 
  of 
  Lower 
  Old 
  .Red 
  Sandstone 
  age, 
  has 
  

   invaded 
  a 
  volcanic 
  and 
  plutonic 
  basic 
  series, 
  probably 
  of 
  Arenig 
  

   age. 
  Tbe 
  phenomena 
  of 
  the 
  junction-surfaces, 
  and 
  of 
  the 
  smaller 
  

   veins, 
  repeat 
  those 
  described 
  by 
  Sollas, 
  Harker, 
  and 
  others 
  ; 
  

   and 
  tbe 
  most 
  extensive 
  intermingling 
  appears 
  to 
  have 
  gone 
  

   on. 
  Even 
  the 
  ferromagnesian 
  constituents 
  of 
  the 
  Siieve 
  Gallion 
  

   granite 
  may 
  possibly 
  result 
  from 
  the 
  process 
  of 
  absorption. 
  Hence 
  

   the 
  intimate 
  intermixtures, 
  so 
  well 
  represented 
  by 
  the 
  Madras 
  

   dykes, 
  may 
  arise 
  from 
  the 
  joint 
  intrusion 
  of 
  materials 
  already 
  

   well 
  worked 
  together 
  and 
  intermingled 
  in 
  the 
  main 
  mass 
  lower 
  

   down. 
  

  

  Mr. 
  W. 
  W. 
  Watts, 
  after 
  ascertaining 
  that 
  the 
  previous 
  speaker 
  was 
  

   inclined 
  to 
  regard 
  the 
  biotite 
  and 
  hornblende 
  of 
  the 
  Siieve 
  Gallion 
  

   granite 
  as 
  having 
  been 
  derived 
  from 
  a 
  basic 
  rock, 
  pointed 
  out 
  that 
  in 
  

   the 
  rocks 
  described 
  by 
  Harker 
  from 
  Skye 
  the 
  hornblende 
  derived 
  from 
  

   the 
  augite 
  of 
  gabbro 
  was 
  quite 
  distinguishable 
  from 
  tbe 
  indigenous 
  

   hornblende 
  of 
  the 
  granopbyre. 
  It 
  was 
  therefore 
  certain 
  that 
  some 
  

   of 
  the 
  ferromagnesian 
  minerals 
  in 
  granitic 
  rocks 
  were 
  original, 
  and 
  

   not 
  derived 
  at 
  the 
  expense 
  of 
  basic 
  rocks. 
  

  

  Mr. 
  Rtjtley 
  agreed 
  with 
  a 
  previous 
  speaker 
  in 
  thinking 
  that 
  the 
  

   Author 
  was 
  probably 
  right 
  in 
  his 
  conclusion 
  that 
  the 
  micropegmatitic 
  

   matter 
  was 
  not 
  of 
  secondary 
  origin, 
  but 
  doubted 
  whether 
  ' 
  augite- 
  

   diorite'* 
  was 
  a 
  perfectly 
  satisfactory 
  name 
  to 
  apply 
  to 
  a 
  rock 
  such 
  as 
  

   that 
  described. 
  Tbe 
  diagram 
  did 
  not 
  indicate 
  a 
  truly 
  ophitic 
  

   structure, 
  although 
  it 
  showed 
  an 
  approximation 
  to 
  it. 
  

  

  Rev. 
  J. 
  F. 
  Blake 
  asked 
  whether 
  in 
  this 
  particular 
  case 
  the 
  Author 
  

   had 
  definitely 
  proved 
  to 
  his 
  own 
  satisfaction 
  what 
  were 
  the 
  actual 
  

   mineral 
  constituents 
  of 
  the 
  ' 
  micropegmatite.' 
  If 
  one 
  of 
  them 
  was 
  

   optically 
  continuous 
  with 
  a 
  plagioclase, 
  and 
  there 
  were 
  also 
  ortho- 
  

   clase 
  and 
  quartz, 
  this 
  would 
  make 
  three 
  minerals 
  ; 
  but 
  he 
  had 
  not 
  

   been 
  able 
  to 
  gather 
  from 
  the 
  reading 
  of 
  the 
  paper 
  anything 
  definite 
  

   on 
  the 
  question. 
  He 
  also 
  enquired 
  why 
  the 
  optical 
  continuity 
  

   of 
  part 
  of 
  the 
  micropegmatite 
  with 
  the 
  neighbouring 
  plagioclase 
  

   proved 
  it 
  to 
  be 
  of 
  the 
  same 
  general 
  age, 
  when 
  similar 
  accretions 
  

   were 
  found 
  round 
  quartz-grains 
  which 
  meanwhile 
  had 
  been 
  rolled 
  

   on 
  the 
  sea-shore. 
  

  

  Mr. 
  J. 
  J. 
  H. 
  Teall 
  and 
  Mr. 
  P. 
  N. 
  Datta 
  also 
  spoke. 
  

  

  Prof. 
  Jtjdd 
  stated 
  that 
  he 
  had 
  been 
  in 
  communication 
  with 
  

   Prof. 
  Sollas, 
  who 
  unfortunately 
  was 
  not 
  able 
  to 
  attend 
  and 
  take 
  

   part 
  in 
  the 
  discussion 
  of 
  this 
  paper. 
  Prof. 
  Sollas, 
  from 
  the 
  perusal 
  

   of 
  the 
  abstract 
  and 
  an 
  examination 
  of 
  a 
  slide 
  of 
  the 
  Madras 
  rock 
  

   forwarded 
  to 
  him, 
  had 
  been 
  able 
  to 
  supply 
  the 
  following 
  contribution 
  

   to 
  the 
  discussion, 
  which, 
  by 
  the 
  permission 
  of 
  the 
  President, 
  was 
  

   read 
  : 
  — 
  

  

  