﻿44 
  Smyth, 
  Jr. 
  — 
  Composition 
  of 
  the 
  Alkaline 
  Rocks 
  

  

  Thus, 
  the 
  alkaline 
  magmas 
  must 
  tend 
  more 
  than 
  the 
  subalka- 
  

   line 
  magmas, 
  to 
  separate 
  into 
  fractions 
  of 
  diverse 
  composition 
  

   and, 
  in 
  view 
  of 
  the 
  elements 
  which 
  concentrate 
  in 
  alkaline 
  

   magmas, 
  some 
  of 
  these 
  fractions 
  will 
  naturally 
  contain 
  rare 
  

   minerals. 
  Moreover, 
  the 
  production 
  of 
  small 
  fractions 
  excep- 
  

   tionally 
  high 
  in 
  alkalies 
  necessarily 
  implies 
  the 
  production 
  of 
  

   corresponding 
  fractions 
  of 
  complementary 
  composition, 
  and 
  

   therefore 
  high 
  in 
  other 
  constituents. 
  How 
  closely 
  these 
  con- 
  

   clusions 
  are 
  in 
  harmony 
  with 
  well-known 
  facts, 
  it 
  is 
  hardly 
  

   necessary 
  to 
  say, 
  since 
  the 
  great 
  range 
  of 
  chemical 
  and 
  miner- 
  

   alogical 
  composition 
  shown 
  by 
  alkaline 
  rocks 
  in 
  limited 
  areas, 
  

   the 
  frequent 
  occurrence, 
  in 
  them, 
  of 
  rare 
  minerals 
  and 
  the 
  

   not 
  uncommon 
  presence 
  of 
  highly 
  calcic 
  rocks, 
  are 
  among 
  the 
  

   familiar 
  facts 
  of 
  petrology. 
  

  

  Of 
  interest 
  in 
  this 
  connection 
  is 
  Yogt's* 
  statement 
  that, 
  in 
  

   so 
  far 
  as 
  limited 
  miscibility 
  may 
  play 
  a 
  part 
  in 
  magmatic 
  differ- 
  

   entiation, 
  it 
  would 
  be 
  most 
  likely 
  to 
  occur 
  in 
  rocks 
  rich 
  in 
  

   mineralizers. 
  

  

  Thus, 
  we 
  arrive 
  at 
  the 
  conclusion 
  that 
  the 
  pegmatite 
  dikes 
  

   of 
  such 
  a 
  region 
  as 
  the 
  alkaline 
  province 
  of 
  Christiania 
  are 
  but 
  

   the 
  last 
  step 
  in 
  a 
  somewhat 
  discontinuous 
  but 
  still 
  causally 
  

   connected 
  series 
  of 
  operations, 
  differing 
  vastly 
  in 
  degree 
  rather 
  

   than 
  in 
  kind, 
  starting 
  in 
  the 
  normal 
  subalkaline 
  magma 
  and 
  

   effected 
  primarily 
  through 
  the 
  agency 
  of 
  mineralizers, 
  subject 
  

   to 
  secondary 
  mechanical 
  control. 
  

  

  It 
  is 
  hardly 
  necessary 
  to 
  say 
  that 
  this 
  hypothesis 
  has 
  much 
  in 
  

   common 
  with 
  the 
  views 
  promulgated 
  by 
  the 
  French 
  petrologistsf 
  

   in 
  so 
  far 
  as 
  the 
  potency 
  of 
  mineralizers 
  in 
  igneous 
  activities, 
  

   and 
  especially 
  in 
  connection 
  with 
  magmatic 
  differentiation, 
  is 
  

   concerned. 
  

  

  On 
  the 
  other 
  hand, 
  it 
  differs 
  materially 
  from 
  Becke's 
  hypoth- 
  

   esis 
  of 
  a 
  primordial 
  gaseous 
  separation, 
  in 
  a 
  vertical 
  sense, 
  of 
  

   alkaline 
  and 
  subalkaline 
  materials. 
  From 
  Harker's 
  hypothesis, 
  

   it 
  differs 
  essentially 
  in 
  ascribing 
  the 
  chief 
  function 
  to 
  mineral- 
  

   izers 
  rather 
  than 
  to 
  mechanical 
  conditions 
  and 
  in 
  regarding 
  

   alkaline 
  magmas 
  as 
  local 
  derivatives 
  of 
  the 
  universal 
  subalkaline 
  

   magma, 
  instead 
  of 
  assuming 
  separation 
  of 
  the 
  two 
  types 
  by 
  a 
  

   horizontal 
  differentiation 
  of 
  regional 
  magnitude. 
  Jensen's 
  

   hypothesis 
  is 
  based 
  upon 
  melting 
  of 
  early 
  alkaline 
  and 
  saline 
  

   sediments, 
  with 
  some 
  assimilation 
  and 
  mixing, 
  and 
  is, 
  thus, 
  

   essentially 
  different 
  from 
  the 
  views 
  here 
  advanced. 
  Daly's 
  

   hypothesis 
  has 
  much 
  in 
  common 
  with 
  the 
  writer's, 
  though 
  

   based 
  upon 
  assimilation, 
  but 
  the 
  assimilation 
  postulated 
  is 
  

   of 
  limestone 
  and 
  it 
  is 
  to 
  the 
  carbon-dioxide 
  of 
  this 
  rock 
  that 
  

  

  * 
  J. 
  H. 
  L. 
  Vogt, 
  Die 
  SilikatschmelzlosuDgen, 
  II, 
  p. 
  229, 
  1904. 
  

   fCf. 
  A. 
  Michel-Levy 
  : 
  Note 
  sur 
  la 
  classification 
  des 
  Magmas 
  des 
  Roches 
  

   Eruptive, 
  Bull. 
  Soc. 
  Geol. 
  France 
  (3), 
  xxv, 
  pp. 
  326-377, 
  1897. 
  

  

  