﻿Geology. 
  459 
  

  

  As 
  geology 
  cannot 
  reach 
  very 
  far 
  down 
  into 
  the 
  earth, 
  stocks 
  

   and 
  laccoliths 
  (iu 
  a 
  broad 
  sense 
  any 
  large, 
  deeply 
  consolidated 
  

   mass 
  of 
  magma) 
  must 
  furnish 
  our 
  types. 
  All 
  rocks 
  which 
  can 
  

   be 
  referred 
  to 
  the 
  same 
  magma 
  must 
  belong 
  to 
  the 
  same 
  family. 
  

  

  We 
  have 
  first 
  to 
  distinguish 
  abyssal 
  rocks, 
  then 
  marginal 
  facies, 
  

   then 
  hypabyssal 
  dikes 
  and 
  sheets 
  (including 
  diaschistic 
  and 
  

   aschistic,* 
  in 
  the 
  former 
  complementary 
  types, 
  in 
  the 
  latter 
  main 
  

   rock 
  and 
  salband), 
  lastly 
  flow 
  rocks, 
  pala3otypic 
  and 
  csenotypic, 
  

   diaschistic 
  and 
  aschistic. 
  

  

  Families 
  with 
  the 
  same 
  predominating 
  metallic 
  oxide 
  should 
  

   form 
  one 
  series. 
  Thus 
  there 
  would 
  be 
  as 
  the 
  main 
  families 
  the 
  

   potash, 
  the 
  soda, 
  the 
  lime 
  and 
  the 
  magnesia 
  series 
  ; 
  the 
  alumina 
  

   and 
  iron 
  rocks 
  are 
  doubtful 
  because 
  they 
  are 
  not 
  known 
  to 
  occur 
  

   as 
  stocks 
  or 
  laccoliths. 
  Further 
  there 
  are 
  transition 
  series, 
  the 
  

   potash-soda 
  and 
  the 
  alkali-lime 
  rocks. 
  There 
  are 
  therefore 
  six 
  

   main 
  rock 
  families. 
  As 
  regards 
  silica 
  we 
  should 
  distinguish 
  

   hyperacid, 
  acid, 
  intermediate, 
  basic 
  and 
  ultrabasic. 
  Thus 
  as 
  

   examples 
  we 
  would 
  have 
  

  

  f 
  Hyperacid. 
  Soda-granite. 
  Akerite. 
  

  

  | 
  Acid. 
  Soda-quartz-syenite. 
  Nordmarkite. 
  

  

  Soda 
  Family 
  -j 
  Intermediate 
  J 
  Nepheline-syemte. 
  Foyaite 
  

  

  ( 
  soda-syenite. 
  JLaurvikite. 
  

   (^ 
  Basic. 
  Absent. 
  

  

  ( 
  Hyperacid. 
  Adamellite. 
  

  

  Alkali-lime 
  J 
  Acid. 
  Banatite. 
  

  

  Family 
  j 
  Intermediate. 
  Monzonite. 
  

  

  (_ 
  Basic. 
  Essexite. 
  

  

  f 
  Hyperacid. 
  Tonalite. 
  

  

  T 
  . 
  -n, 
  ., 
  j 
  Acid. 
  Quartz-diorite. 
  

  

  Lime 
  Family 
  -j 
  Intermediate 
  . 
  g 
  iorite 
  . 
  

  

  (_ 
  Basic. 
  Gabbro 
  and 
  Anorthosite. 
  

  

  The 
  families 
  are 
  to 
  be 
  defined 
  by 
  the 
  chemical 
  composition 
  of 
  

   the 
  main 
  rock 
  types, 
  limits 
  of 
  course 
  to 
  be 
  considered. 
  The 
  con- 
  

   nection 
  of 
  aschistic 
  types 
  with 
  abyssal 
  rocks 
  is 
  well 
  known, 
  obvious, 
  

   and 
  not 
  denied 
  by 
  any 
  petrographer. 
  All 
  such 
  aschistic 
  struc- 
  

   ture 
  types 
  should 
  be 
  referred 
  to 
  the 
  related 
  abyssal 
  magma. 
  This 
  

   is 
  generally 
  believed 
  and 
  done. 
  

  

  Diaschistic 
  dikes 
  should 
  also 
  be 
  referred 
  to 
  abyssal 
  magmas 
  

   (rocks) 
  from 
  which 
  they 
  are 
  derived. 
  This 
  will 
  be 
  the 
  main 
  diffi- 
  

   culty 
  with 
  most 
  petrographers. 
  It 
  is 
  proved 
  by 
  geological 
  obser- 
  

   vation 
  that 
  they 
  are 
  consanguineous 
  ; 
  South 
  Norway 
  furnishes 
  

   excellent 
  examples 
  which 
  have 
  been 
  studied 
  and 
  described. 
  The 
  

   relationships 
  are 
  very 
  clear 
  for 
  the 
  hyperacid, 
  acid 
  and 
  basic 
  fam- 
  

   ilies; 
  only 
  the 
  intermediate 
  ones 
  are 
  difficult 
  to 
  decipher, 
  such 
  as 
  

   those 
  of 
  the 
  nepheline-syenites. 
  

  

  The 
  differentiated 
  (e. 
  g. 
  dike) 
  types 
  can 
  have 
  quite 
  different 
  

   compositions 
  (chemical 
  and 
  mineralogical) 
  from 
  the 
  main 
  type. 
  

   This 
  is 
  quite 
  analogous 
  with 
  the 
  classifications 
  brought 
  out 
  by 
  

  

  * 
  For 
  the 
  explanation 
  of 
  these 
  terms 
  conf. 
  Brogger 
  Grorudit-Tinguait 
  Serie 
  

   1894, 
  p. 
  155. 
  

  

  