﻿Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  35 
  

  

  in 
  the 
  belief 
  that 
  the 
  earth 
  has 
  been 
  fluid, 
  not 
  indeed 
  at 
  any 
  

   one 
  time 
  from 
  center 
  to 
  its 
  present 
  surface, 
  but 
  at 
  least 
  to 
  a 
  

   great 
  depth 
  from 
  the 
  temporary 
  surface 
  of 
  the 
  growing 
  globe. 
  

   Yet 
  the 
  earth 
  is 
  clearly 
  not 
  a 
  homogeneous 
  mass, 
  nor 
  is 
  it 
  a 
  

   system 
  of 
  concentric 
  shells, 
  each 
  homogeneous. 
  9 
  The 
  mere 
  

   fact 
  that 
  one 
  hemisphere 
  is 
  almost 
  entirely 
  covered 
  by 
  water 
  

   shows 
  that 
  the 
  globe 
  is 
  of 
  greater 
  density 
  below 
  this 
  great 
  

   ocean 
  than 
  beneath 
  the 
  opposite 
  continental 
  surface. 
  Were 
  

   the 
  shells 
  homogeneous 
  no 
  continents 
  could 
  protrude 
  above 
  the 
  

   sea. 
  "Were 
  the 
  earth 
  of 
  uniform 
  composition 
  no 
  mountain 
  

   ranges 
  could 
  stand 
  above 
  the 
  plains. 
  Were 
  the 
  material 
  below 
  

   the 
  plains 
  uniformly 
  distributed 
  there 
  could 
  be 
  no 
  anomalies 
  

   of 
  gravity 
  such 
  as 
  occur 
  near 
  Moscow, 
  in 
  Kansas, 
  and 
  else- 
  

   where. 
  The 
  distribution 
  of 
  feldspars 
  in 
  the 
  western 
  part 
  of 
  

   this 
  continent 
  shows 
  lack 
  of 
  homogeneity, 
  for 
  on 
  the 
  Pacific 
  

   slope 
  potash 
  feldspars 
  are 
  marvelously 
  rare. 
  No 
  trachyte 
  and 
  

   extremely 
  little 
  typical 
  granite 
  is 
  known 
  from 
  the 
  Wahsatch 
  

   range 
  to 
  the 
  Pacific 
  ocean. 
  The 
  distribution 
  of 
  metallic 
  ores 
  

   shows 
  heterogeneity. 
  Much 
  more 
  than 
  90 
  per 
  cent 
  of 
  the 
  

   known 
  tin 
  ores 
  of 
  the 
  world 
  lie 
  in 
  a 
  belt 
  stretching 
  from 
  the 
  

   straits 
  of 
  Malacca 
  to 
  Tasmania. 
  There 
  has 
  been 
  deposition 
  of 
  

   mercurial 
  ores 
  in 
  this 
  belt 
  also 
  ; 
  but 
  their 
  quantity 
  is 
  insignifi- 
  

   cant. 
  A 
  belt 
  of 
  quicksilver 
  deposits 
  extends 
  from 
  British 
  

   Columbia 
  to 
  Chili. 
  In 
  this 
  belt 
  there 
  is 
  tinstone 
  at 
  many 
  

   points, 
  but 
  the 
  total 
  product 
  of 
  tin 
  on 
  this 
  belt 
  is 
  scarcely 
  

   worth 
  mentioning. 
  I 
  can 
  only 
  infer 
  from 
  these 
  facts 
  that 
  

   quicksilver 
  is 
  an 
  extremely 
  subordinate 
  component 
  of 
  the 
  earth 
  

   in 
  the 
  Australasian 
  region 
  and 
  that 
  the 
  globe 
  contains 
  little 
  tin 
  

   along 
  the 
  Cordilleran 
  belt. 
  It 
  is 
  needless 
  to 
  observe 
  that 
  in 
  

   almost 
  any 
  small 
  area 
  the 
  rocks 
  show 
  marked 
  variations 
  or 
  that 
  

   two 
  hand 
  specimens 
  from 
  the 
  same 
  locality 
  are 
  rarely 
  indis- 
  

   tinguishable. 
  Deserving 
  of 
  special 
  mention, 
  however, 
  are 
  the 
  

   striped 
  rhyolites, 
  the 
  banded 
  gabbros 
  studied 
  by 
  Sir 
  Archibald 
  

   Geikie 
  and 
  Mr. 
  Teall, 
  and 
  the 
  ribbon 
  gneisses 
  so 
  abundant, 
  for 
  

   example, 
  in 
  the 
  southern 
  Appalachians. 
  The 
  rhyolite 
  at 
  least 
  

   has 
  been 
  fluid, 
  and 
  most 
  geologists 
  consider 
  gabbroitic 
  and 
  

   granitic 
  magmas 
  as 
  fluids. 
  The 
  diffusion 
  exhibited 
  in 
  these 
  

   cases 
  is 
  slight 
  and 
  sometimes 
  hardly 
  perceptible 
  to 
  the 
  naked 
  

   eye, 
  yet 
  it 
  is 
  scarcely 
  supposable 
  that 
  these 
  bands 
  were 
  not 
  in 
  

   contact 
  for 
  days 
  at 
  least 
  in 
  their 
  mobile 
  state. 
  Now 
  my 
  hypo- 
  

   thetical 
  lava 
  would 
  diffuse 
  to 
  the 
  depth 
  of 
  a 
  millimeter 
  in 
  three 
  

   or 
  four 
  hours. 
  Hence 
  these 
  sharply 
  banded 
  rocks 
  must 
  be 
  

   much 
  less 
  diffusible 
  than 
  my 
  assumed 
  lava 
  and 
  the 
  diffusivity 
  

   of 
  the 
  granular 
  rocks 
  and 
  their 
  fluidity 
  would 
  scarcely 
  exceed 
  

   zero.* 
  Thus 
  from 
  the 
  surface 
  of 
  the 
  globe 
  to 
  its 
  minutest 
  

  

  * 
  Banding 
  such 
  as 
  is 
  found 
  in 
  gueiss 
  and 
  rhyolite 
  could 
  not 
  result 
  directly 
  from 
  

   segregation 
  on 
  Soret's 
  methods 
  or 
  by 
  difference 
  of 
  pressure, 
  for 
  these 
  processes 
  

  

  