﻿116 
  NEW 
  TORK 
  STATE 
  MUSEUM 
  

  

  ers 
  of 
  different 
  densities, 
  the 
  rarer 
  substances 
  to 
  some 
  extent 
  

   occupying 
  the 
  outer 
  portion 
  of 
  the 
  mass. 
  

  

  If, 
  as 
  this 
  hypothesis 
  suggests, 
  our 
  earth 
  is 
  an 
  integral 
  part 
  of 
  

   the 
  solar 
  system 
  we 
  should 
  expect 
  to 
  find 
  its 
  component 
  elements 
  

   in 
  the 
  sun 
  and 
  in 
  the 
  other 
  heavenly 
  bodies, 
  and 
  this 
  expectation 
  

   is 
  confirmed 
  by 
  two 
  distinct 
  sources 
  of 
  information. 
  Chemical 
  

   analysis 
  of 
  the 
  meteorites 
  which 
  fall 
  to 
  earth 
  shows 
  that 
  these 
  

   bodies 
  contain 
  many 
  minerals 
  which 
  occur 
  in 
  the 
  earth's 
  crust** 
  

   and 
  that 
  they 
  do 
  not 
  contain 
  any 
  elements 
  which 
  are 
  unknown 
  

   on 
  earth. 
  Of 
  late 
  the 
  application 
  of 
  the 
  spectroscope 
  to 
  the 
  

   study 
  of 
  the 
  sun 
  and 
  stars 
  has 
  established 
  the 
  fact 
  that 
  these 
  

   celestial 
  bodies 
  are 
  largely 
  composed 
  of 
  the 
  elements 
  already 
  

   known 
  on 
  earth. 
  There 
  are 
  however 
  some 
  lines 
  in 
  the 
  solar 
  

   and 
  stellar 
  spectra 
  which 
  are 
  not 
  matched 
  by 
  the 
  lines 
  in 
  any 
  

   terrestrial 
  spectrum. 
  

  

  The 
  conclusion 
  to 
  which 
  we 
  are 
  led 
  by 
  the 
  nebular 
  hypothesis, 
  

   viz.: 
  that 
  the 
  earth 
  originated 
  as 
  a 
  rotating 
  mass 
  of 
  incandescent 
  

   gas, 
  is 
  corroborated 
  by 
  its 
  present 
  form, 
  which 
  is 
  that 
  of 
  a 
  

   spheroid 
  of 
  rotation 
  or 
  of 
  a 
  plastic 
  body 
  which, 
  by 
  rotation, 
  has 
  

   become 
  flattened 
  at 
  the 
  poles. 
  The 
  difference 
  between 
  the 
  polar 
  

   and 
  equatorial 
  diameters 
  of 
  the 
  earth 
  is 
  about 
  27 
  miles. 
  

  

  Chemical 
  science 
  has 
  established 
  the 
  fact 
  that 
  all 
  forms 
  of 
  

   matter 
  are 
  composed 
  of 
  one 
  or 
  more 
  of 
  the 
  elementary 
  substances 
  

   or 
  elements, 
  of 
  which 
  there 
  are 
  74. 
  These 
  are 
  all 
  found 
  either 
  

   in 
  the 
  earth's 
  crust, 
  or 
  in 
  its 
  atmosphere; 
  they 
  also 
  occur 
  in 
  the 
  

   sun, 
  stars 
  and 
  other 
  heavenly 
  bodies. 
  Most 
  of 
  these 
  elements 
  are 
  

   very 
  rare 
  and 
  do 
  not 
  come 
  to 
  the 
  notice 
  of 
  the 
  geologist. 
  Only 
  

   11 
  are 
  important 
  as 
  constituents 
  of 
  the 
  earth's 
  crust. 
  These 
  more 
  

   common 
  elements 
  are 
  given 
  in 
  the 
  following 
  table^ 
  with 
  their 
  

   proportionate 
  percentages 
  as 
  components 
  of 
  the 
  earth's 
  crust: 
  

  

  Oxygen 
  50 
  

  

  Silicon 
  25 
  

  

  Aluminum 
  10 
  

  

  Calcium 
  4.5 
  

  

  Magnesium 
  3.5 
  

  

  Sodium 
  2 
  

  

  a 
  The 
  crust 
  is 
  the 
  superficial 
  portion 
  of 
  the 
  earth. 
  Preitwich 
  Geology, 
  p. 
  10. 
  

  

  