﻿Lindgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  279 
  

  

  proposal 
  to 
  establish 
  the 
  new 
  family 
  of 
  the 
  monzonites 
  inter- 
  

   mediate 
  between 
  the 
  syenites 
  and 
  the 
  diorites, 
  and 
  that 
  of 
  the 
  

   quartz-monzonites 
  intermediate 
  between 
  the 
  granites 
  and 
  the 
  

   quartz-diorites. 
  The 
  kernel 
  of 
  the 
  definition 
  of 
  these 
  rocks 
  is 
  

   contained 
  in 
  the 
  following 
  words 
  :* 
  " 
  Das 
  wirklich 
  character- 
  

   ische 
  bei 
  diesen 
  Gesteinen, 
  ist 
  dass 
  sie 
  in 
  der 
  Kegel 
  Orthoklas 
  

   und 
  Plagioklas 
  ungefahr 
  gleich 
  reichlich 
  oder 
  jedenfalls 
  beide 
  

   reichlich 
  fiihren." 
  On 
  the 
  same 
  page 
  we 
  read 
  " 
  Die 
  Monzonite 
  

   characterisiren 
  sich 
  dadnrch 
  dass 
  sie 
  weder 
  zu 
  den 
  Orthoklas- 
  

   Gesteinen 
  noch 
  zu 
  den 
  Plagioklas- 
  Gesteinen, 
  sondern 
  zu 
  einer 
  

   Uebergangsgruppe 
  zwischen 
  beiden 
  gehoren, 
  sie 
  sind 
  eben 
  : 
  

   Orthoklas-Plagioklas-Gesteine." 
  In 
  the 
  same 
  place 
  Prof. 
  

   Brogger 
  states 
  that 
  in 
  his 
  opinion,. 
  in 
  order 
  to 
  apply 
  the 
  name 
  

   diorite, 
  the 
  soda-lime 
  feldspars 
  must 
  strongly 
  predominate 
  ; 
  in 
  

   granite, 
  on 
  the 
  other 
  hand, 
  the 
  alkali 
  feldspars 
  must 
  strongly 
  

   predominate 
  or 
  (see 
  footnote) 
  the 
  plagioclase 
  must 
  be 
  so 
  acid 
  

   that 
  the 
  rock 
  is 
  very 
  poor 
  in 
  lime. 
  

  

  In 
  the 
  above 
  definition 
  there 
  is 
  no 
  special 
  limit 
  assigned 
  to 
  

   the 
  soda- 
  lime 
  feldspars, 
  so 
  that 
  the 
  permissible 
  variation 
  becomes 
  

   rather 
  large. 
  It 
  must 
  be 
  apparent, 
  however, 
  that 
  the 
  author 
  

   intended 
  the 
  rock 
  in 
  its 
  most 
  typical 
  development 
  to 
  be 
  placed 
  

   exactly 
  half 
  way 
  between 
  the 
  granites 
  and 
  the 
  quartz-diorites 
  so 
  

   far 
  as 
  the 
  feldspars 
  were 
  concerned. 
  This 
  view 
  is 
  corroborated 
  

   by 
  the 
  fact 
  that 
  of 
  the 
  two 
  calculated 
  analyses 
  given, 
  the 
  first 
  

   — 
  a 
  monzonite 
  — 
  has 
  30 
  per 
  cent 
  orthoclase 
  and 
  32 
  per 
  cent 
  

   soda-lime 
  feldspar 
  (Ab 
  3 
  An 
  2 
  ) 
  and 
  the 
  second 
  — 
  a 
  quartz-mon- 
  

   zonite 
  — 
  (p. 
  62, 
  1. 
  c), 
  35*5 
  per 
  cent 
  orthoclase 
  and 
  31*5 
  per 
  cent 
  

   Ab 
  2 
  An 
  3 
  . 
  

  

  Thus 
  the 
  term 
  quartz-monzonite 
  becomes 
  a 
  central 
  type 
  

   embracing 
  a 
  series 
  of 
  rocks 
  on 
  each 
  side 
  of 
  the 
  definition. 
  

   Just 
  how 
  far 
  Brogger 
  intended 
  to 
  extend 
  these 
  limits 
  is 
  not 
  

   clearly 
  stated. 
  

  

  There 
  is 
  undoubtedly 
  ample 
  justification 
  for 
  the 
  introduc- 
  

   tion 
  of 
  the 
  term 
  quartz-monzonite 
  as 
  defined 
  by 
  Brogger, 
  but 
  

   reasonable 
  limits 
  should 
  be 
  assigned 
  to 
  it. 
  It 
  would 
  mani- 
  

   festly 
  be 
  incorrect 
  to 
  define 
  a 
  family 
  as 
  having 
  approximately 
  

   equal 
  amounts 
  of 
  orthoclase 
  and 
  soda-lime 
  feldspars 
  and 
  then 
  

   include 
  in 
  it 
  rocks 
  having 
  three 
  or 
  four 
  times 
  as 
  much 
  of 
  one 
  

   as 
  of 
  the 
  other. 
  The 
  definition 
  of 
  granodiorite 
  would 
  give 
  it, 
  

   say 
  from 
  . 
  8 
  per 
  cent 
  to 
  20 
  per 
  cent 
  orthoclase. 
  In 
  the 
  quartz- 
  

   monzonites 
  I 
  would 
  give 
  this 
  mineral 
  a 
  range 
  from 
  20 
  per 
  cent 
  

   to 
  40 
  per 
  cent, 
  all 
  in 
  an 
  assumed 
  total 
  of 
  60 
  per 
  cent 
  feldspars. 
  

   The 
  rocks 
  containing 
  more 
  than 
  ttO 
  per 
  cent 
  orthoclase 
  would 
  

   then 
  be 
  classed 
  as 
  granites, 
  there 
  being 
  scarcely 
  room 
  for 
  

   another 
  family 
  between 
  the 
  quartz-monzonites 
  and 
  the 
  granites. 
  

  

  *1. 
  c. 
  p. 
  21. 
  

  

  