﻿36 
  Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  

  

  portions 
  there 
  are 
  clear 
  indications 
  of 
  heterogeneity, 
  notwith- 
  

   standing 
  that 
  similar 
  rocks 
  and 
  similar 
  series 
  of 
  rocks 
  occur 
  in 
  

   widely 
  dispersed 
  localities. 
  

  

  Is 
  there 
  any 
  valid 
  indication 
  that 
  uniformity 
  ever 
  reigned 
  ? 
  

   It 
  used 
  to 
  be 
  thought 
  that 
  the 
  Archaean 
  rocks 
  were 
  uniform, 
  

   but 
  it 
  is 
  well 
  known 
  now 
  that 
  they 
  are 
  not 
  so. 
  The 
  early 
  

   eruptions 
  and 
  intrusions 
  seem 
  quite 
  as 
  diverse 
  as 
  the 
  modern 
  

   ones, 
  excepting 
  so 
  far 
  as 
  original 
  differences 
  are 
  masked 
  by 
  

   metamorphism. 
  The 
  theory 
  of 
  the 
  permanence 
  of 
  continental 
  

   areas 
  has 
  many 
  very 
  strong 
  supporters, 
  and 
  that 
  land 
  areas 
  have 
  

   existed 
  since 
  the 
  Cambrian 
  seems 
  certain. 
  The 
  mountain 
  sys- 
  

   tem 
  of 
  the 
  world 
  in 
  its 
  larger 
  features 
  appears 
  to 
  have 
  been 
  

   outlined 
  during 
  the 
  Archaean, 
  and 
  there 
  are 
  observations 
  indi- 
  

   cating 
  a 
  highly 
  accentuated 
  topography 
  even 
  in 
  those 
  days. 
  

   Were 
  the 
  indications 
  of 
  heterogeneous 
  composition 
  confined 
  to 
  

   the 
  immediate 
  neighborhood 
  of 
  the 
  earth's 
  surface, 
  it 
  might 
  be 
  

   maintained 
  that 
  these 
  inequalities 
  had 
  been 
  brought 
  about 
  since 
  

   consolidation, 
  but 
  everything 
  tends 
  to 
  show 
  that 
  only 
  the 
  shell 
  

   of 
  the 
  earth 
  next 
  to 
  the 
  surface 
  and 
  a 
  few 
  miles 
  in 
  depth 
  par- 
  

   take 
  sensibly 
  in 
  orogenic 
  movements, 
  while 
  several 
  of 
  the 
  evi- 
  

   dences 
  of 
  heterogeneity 
  point 
  to 
  inequalities 
  at 
  great 
  depth. 
  

  

  Uniformity 
  unattainable. 
  — 
  If 
  the 
  earth 
  condensed 
  from 
  a 
  

   nebulous 
  ring, 
  it 
  is 
  fairly 
  inconceivable 
  that 
  the 
  successive 
  

   shells 
  of 
  the 
  growing 
  mass 
  should 
  each 
  have 
  been 
  uniform 
  in 
  

   composition 
  ; 
  and 
  if 
  the 
  origin 
  of 
  the 
  earth 
  is 
  a 
  ring 
  thrown 
  

   off 
  from 
  the 
  sun, 
  the 
  coalescence 
  of 
  this 
  ring 
  to 
  a 
  globe 
  can- 
  

   not 
  have 
  resulted 
  immediately 
  in 
  uniform 
  distribution 
  of 
  mat- 
  

   ter. 
  The 
  sun 
  spots 
  show 
  that 
  the 
  sun 
  is 
  not 
  even 
  yet 
  an 
  

   aggregate 
  of 
  shells 
  each 
  uniform 
  in 
  composition. 
  The 
  exterior 
  

   layer 
  of 
  the 
  globe 
  must 
  have 
  retained 
  such 
  fluidity 
  as 
  it 
  pos- 
  

   sessed 
  for 
  a 
  very 
  long 
  time, 
  and 
  must 
  have 
  passed 
  by 
  insensible 
  

   gradations 
  through 
  every 
  temperature 
  between 
  the 
  initial 
  one 
  

   and 
  that 
  of 
  consolidation. 
  Had 
  the 
  various 
  component 
  por- 
  

   tions 
  of 
  this 
  layer 
  been 
  of 
  large 
  size, 
  of 
  low 
  viscosity, 
  and 
  not 
  

   miscible 
  with 
  one 
  another, 
  they 
  would 
  have 
  arranged 
  them- 
  

   selves 
  in 
  the 
  order 
  of 
  density 
  quite 
  irrespective 
  of 
  chemical 
  

   composition. 
  If 
  the 
  masses 
  were 
  viscous, 
  however, 
  nothing 
  

   like 
  a 
  perfect 
  separation 
  according 
  to 
  density 
  could 
  occur 
  in 
  

  

  can 
  lead 
  only 
  to 
  very 
  gradual 
  transitions. 
  Banding 
  might 
  conceivably 
  result 
  from 
  

   such 
  a 
  segregation 
  followed 
  by 
  active 
  stirring, 
  but 
  only 
  on 
  condition 
  that 
  stirring 
  

   was 
  immediately 
  followed 
  by 
  solidification, 
  for 
  otherwise 
  diffusion 
  would 
  restore 
  

   homogeneity. 
  Separation 
  of 
  a 
  magma 
  into 
  immiscible 
  portions 
  followed 
  by 
  active 
  

   stirring 
  might 
  also 
  produce 
  banding, 
  but 
  again 
  only 
  on 
  condition 
  of 
  immediate 
  

   consolidation, 
  since 
  otherwise 
  separation 
  into 
  two 
  layers 
  would 
  again 
  take 
  place 
  

   and 
  much 
  more 
  rapidly 
  than 
  at 
  first. 
  

  

  Miscible 
  substances 
  in 
  contact 
  which 
  do 
  not 
  diffuse 
  at 
  a 
  finite 
  rate 
  can 
  have 
  no 
  

   sensible 
  vapor 
  tension 
  and 
  must 
  be 
  solids 
  or 
  ultra 
  viscous 
  fluids. 
  Immiscible 
  

   fluids 
  must 
  have 
  a 
  perfectly 
  sharp 
  contact 
  like 
  that 
  between 
  a 
  lead 
  button 
  in 
  aD 
  

   assayer's 
  crucible 
  and 
  the 
  enveloping 
  slag. 
  

  

  