﻿.Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  39 
  

  

  primitive, 
  un 
  mingled, 
  unsegregated 
  masses 
  is 
  correct, 
  a 
  good 
  

   many 
  of 
  these 
  must 
  have 
  the 
  composition 
  of 
  augite-andesite 
  ; 
  

   for 
  this 
  as 
  well 
  as 
  several 
  other 
  simple 
  rock 
  types 
  has 
  issued 
  at 
  

   most 
  distant 
  points 
  with 
  almost 
  constant 
  characteristics. 
  Fusion 
  

   may, 
  however, 
  also 
  affect 
  two 
  or 
  more 
  diverse 
  masses 
  and 
  then 
  

   eruption 
  tends 
  to 
  mingle 
  them. 
  Ejection 
  through 
  pipes 
  or 
  fis- 
  

   sures 
  must 
  indeed 
  be 
  a 
  most 
  efficient 
  stirring 
  process, 
  and 
  since 
  

   relief 
  of 
  pressure 
  is 
  accompanied 
  by 
  depression 
  of 
  the 
  melting 
  

   point, 
  different 
  magmas 
  thus 
  ejected 
  are 
  superheated 
  and 
  may 
  

   mingle 
  to 
  an 
  observable 
  extent 
  by 
  diffusion 
  before 
  they 
  finally 
  

   consolidate. 
  In 
  such 
  cases 
  one 
  would 
  probably 
  find 
  two 
  (or 
  

   more) 
  rock 
  types 
  accompanied 
  by 
  mixtures 
  of 
  variable 
  compo- 
  

   sition. 
  Again, 
  a 
  fissure 
  through 
  which 
  different 
  types 
  were 
  

   extruded 
  successively 
  or 
  in 
  mixture 
  might 
  at 
  the 
  close 
  of 
  the 
  

   eruption 
  be 
  filled 
  with 
  a 
  single 
  type 
  or 
  with 
  a 
  mixture. 
  If 
  

   such 
  a 
  mixture 
  were 
  at 
  all 
  intimate, 
  diffusion 
  would 
  mask 
  the 
  

   original 
  differences 
  and 
  the 
  case 
  would 
  be 
  one 
  of 
  apparent 
  tran- 
  

   sition.* 
  

  

  Possibly 
  some 
  of 
  the 
  observed 
  occurrences 
  which 
  have 
  led 
  

   to 
  the 
  hypothesis 
  of 
  differentiation 
  are 
  really 
  of 
  this 
  character, 
  

   for 
  I 
  think 
  it 
  has 
  been 
  shown 
  in 
  the 
  foregoing 
  pages 
  both 
  that 
  

   transitions 
  can 
  be 
  explained 
  on 
  the 
  hypothesis 
  of 
  primitive 
  

   heterogeneity 
  and 
  that 
  the 
  explanation 
  of 
  differentiation 
  itself 
  

   presents 
  formidable 
  difficulties. 
  I 
  do 
  not 
  see 
  why 
  it 
  should 
  be 
  

   necessary 
  or 
  desirable 
  to 
  assume 
  that 
  in 
  the 
  early 
  history 
  of 
  the 
  

   globe 
  the 
  vast 
  shell 
  from 
  which 
  eruptions 
  issue 
  was 
  reduced 
  to 
  

   substantial 
  uniformity. 
  Experience 
  affords 
  no 
  analogy 
  in 
  sup- 
  

   port 
  of 
  such 
  an 
  assumption 
  nor 
  has 
  any 
  theory 
  been 
  propounded 
  

   which 
  will 
  account 
  for 
  it. 
  

  

  If 
  primitive 
  heterogeneity 
  is 
  still 
  an 
  important 
  feature 
  in 
  

   the 
  earth's 
  structure, 
  and 
  if 
  unmingled 
  magmas 
  represent 
  

   primitive 
  differences, 
  the 
  labors 
  of 
  lithologists 
  would 
  naturally 
  

   be 
  directed 
  to 
  detecting 
  these 
  original 
  types. 
  These 
  would 
  

   probably 
  be 
  recognizable 
  by 
  their 
  wide 
  distribution 
  and 
  con- 
  

   stant 
  character. 
  Then 
  areas 
  of 
  rapid 
  variation 
  would 
  be 
  

   regarded 
  as 
  representing 
  mere 
  mixtures 
  and 
  it 
  might 
  be 
  possi- 
  

   ble 
  to 
  reduce 
  instead 
  of 
  increasing 
  the 
  number 
  of 
  rock 
  species. 
  

  

  Abstract. 
  — 
  All 
  known 
  processes 
  by 
  which 
  the 
  segregation 
  or 
  

   differentiation 
  of 
  a 
  fluid 
  magma 
  could 
  take 
  place 
  involve 
  

  

  * 
  The 
  order 
  of 
  mixture 
  and 
  extrusion 
  would 
  seem 
  to 
  depend 
  on 
  many 
  circum- 
  

   stances, 
  among 
  others 
  on 
  the 
  shape 
  of 
  the 
  subterranean 
  reservoirs. 
  If 
  this 
  were 
  

   a 
  cone 
  with 
  its 
  vertex 
  nearest 
  the 
  surface, 
  the 
  disposition 
  of 
  the 
  ejecta 
  would 
  be 
  

   very 
  different 
  from 
  that 
  which 
  would 
  be 
  observed 
  if 
  the 
  reservoir 
  were 
  a 
  flat- 
  

   tened 
  lens 
  with 
  its 
  edge 
  horizontal 
  and 
  a 
  veat 
  on 
  one 
  surface. 
  If 
  each 
  eruption 
  

   represents 
  a 
  separate 
  melting, 
  still 
  other 
  dispositions 
  will 
  result. 
  It 
  appears 
  to 
  

   me 
  anything 
  but 
  remarkable 
  that 
  different 
  observers 
  find 
  eruptions 
  in 
  different 
  

   areas 
  taking 
  different 
  orders. 
  Gradual 
  solidification 
  from 
  fissure 
  walls 
  of 
  dike 
  

   magmas 
  circulating 
  by 
  convection 
  may 
  lead 
  to 
  preponderance 
  of 
  less 
  fusible 
  in- 
  

   gredients 
  near 
  the 
  edges 
  of 
  a 
  solid 
  dike. 
  

  

  