﻿34 
  Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  

  

  Thus 
  in 
  a 
  spherical 
  mass 
  of 
  100 
  m 
  radius, 
  if 
  half 
  of 
  a 
  compo- 
  

   nent 
  were 
  thus 
  to 
  be 
  deposited 
  on 
  the 
  walls, 
  a 
  portion 
  of 
  this 
  

   deposit 
  would 
  have 
  traversed 
  a 
  distance 
  of 
  nearly 
  2l 
  m 
  by 
  

   molecular 
  flow, 
  which 
  would 
  take 
  thousands 
  of 
  years 
  even 
  in 
  

   the 
  case 
  of 
  a 
  solution 
  of 
  bluestone 
  in 
  water. 
  

  

  If 
  the 
  separating 
  fluid 
  does 
  not 
  condense 
  on 
  the 
  sides 
  of 
  the 
  

   enclosing 
  cavity, 
  it 
  must 
  condense 
  somewhat 
  like 
  fog 
  in 
  the 
  

   mass 
  of 
  the 
  fluid. 
  Now 
  in 
  a 
  very 
  fluid 
  mass, 
  like 
  water, 
  the 
  

   larger 
  drops 
  of 
  such 
  a 
  fluid 
  will 
  rise 
  or 
  sink 
  more 
  rapidly 
  than 
  

   the 
  smaller 
  ones, 
  coalescence 
  will 
  occur 
  and 
  the 
  lighter 
  fluid 
  

   may 
  separate 
  out 
  in 
  a 
  layer. 
  But 
  even 
  in 
  the 
  case 
  of 
  a 
  foreign 
  

   material 
  suspended 
  in 
  air 
  viscosity 
  greatly 
  delays 
  such 
  separa- 
  

   tion. 
  The 
  clouds 
  are 
  substantially 
  aggregates 
  of 
  small 
  water 
  

   drops 
  which, 
  because 
  of 
  the 
  viscosity 
  of 
  the 
  air, 
  fall 
  so 
  slowly 
  

   that 
  the 
  slightest 
  current 
  sweeps 
  them 
  along. 
  So, 
  too, 
  dust 
  

   remains 
  suspended 
  in 
  the 
  atmosphere 
  because 
  air 
  is 
  viscous.* 
  

   In 
  fluids 
  such 
  as 
  lava 
  it 
  scarcely 
  seems 
  credible 
  that 
  any 
  exten- 
  

   sive 
  separation 
  of 
  a 
  precipitated 
  immiscible 
  liquid 
  should 
  occur. 
  

   It 
  may 
  be 
  that 
  spherulites 
  and 
  perhaps 
  some 
  phenocrysts 
  are 
  

   crystallized 
  from 
  drops 
  of 
  such 
  liquids. 
  However 
  this 
  may 
  

   be, 
  it 
  is 
  certain 
  that 
  many 
  of 
  the 
  phenocrysts 
  form 
  before 
  

   eruption 
  and 
  remain 
  suspended 
  in 
  the 
  magma 
  in 
  spite 
  of 
  densi- 
  

   ties 
  differing 
  considerably 
  from 
  that 
  of 
  the 
  medium. 
  f 
  Thus 
  

   even 
  in 
  the 
  process 
  of 
  the 
  separation 
  of 
  fluids 
  into 
  immiscible 
  

   or 
  partially 
  miscible 
  fractions 
  I 
  can 
  see 
  no 
  adequate 
  explana- 
  

   tion 
  of 
  rock 
  segregation. 
  Furthermore, 
  if, 
  as 
  seems 
  to 
  follow 
  

   from 
  the 
  law 
  of 
  fusion, 
  magmas 
  are 
  not 
  heated 
  much 
  above 
  

   the 
  melting 
  point, 
  there 
  is 
  but 
  a 
  small 
  range 
  of 
  temperature 
  

   within 
  which 
  such 
  separations 
  could 
  occur 
  and 
  they 
  would 
  be 
  

   correspondingly 
  rare. 
  

  

  Heterogeneity 
  of 
  the 
  earth. 
  — 
  If 
  the 
  physical 
  theory 
  of 
  solu- 
  

   tion 
  fails 
  to 
  account 
  for 
  rock 
  segregation, 
  two 
  alternatives 
  are 
  

   left. 
  Either 
  segregation 
  takes 
  place 
  in 
  accordance 
  with 
  some 
  

   principle 
  of 
  physics 
  as 
  yet 
  undiscovered 
  (ignotum 
  per 
  ignotius), 
  

   or 
  the 
  facts 
  which 
  have 
  led 
  to 
  the 
  hypothesis 
  of 
  segregation 
  

   are 
  capable 
  of 
  a 
  different 
  interpretation 
  not 
  at 
  variance 
  with 
  

   the 
  known 
  properties 
  of 
  matter 
  and 
  compatible 
  with 
  reason- 
  

   able 
  limits 
  to 
  geological 
  time. 
  

  

  So 
  far 
  as 
  I 
  know, 
  all 
  geologists 
  and 
  astronomers 
  are 
  in 
  unison 
  

  

  *The 
  viscosity 
  of 
  media 
  is 
  probably 
  only 
  one 
  of 
  the 
  influences 
  affecting 
  the 
  sub- 
  

   sidence 
  of 
  disseminated 
  fluid 
  or 
  solid 
  particles 
  

  

  \ 
  It 
  is 
  well 
  known 
  that 
  phenocrysts 
  in 
  fresh 
  surface-flows 
  are 
  often 
  bent 
  and 
  

   even 
  broken. 
  Sometimes 
  black 
  borders 
  have 
  formed 
  about 
  hornblendes 
  thus 
  frac- 
  

   tured. 
  Such 
  fractures 
  must 
  have 
  happened 
  during 
  eruption. 
  The 
  lithologist 
  will 
  

   not 
  require 
  to 
  be 
  reminded 
  that 
  phenocrysts 
  of 
  augite 
  and 
  of 
  amphibole 
  with 
  a 
  

   density 
  of 
  say 
  3*25 
  are 
  often 
  of 
  about 
  the 
  same 
  size 
  as 
  those 
  of 
  feldspar 
  with 
  a 
  

   densiiy 
  of 
  say 
  2 
  - 
  65, 
  yet 
  there 
  is 
  as 
  a 
  rule 
  no 
  tendency 
  to 
  the 
  separation 
  of 
  the 
  

   lighter 
  and 
  heavier 
  phenocrysts 
  into 
  distinct 
  layers. 
  

  

  