﻿COMPONENTS 
  OF 
  THE 
  EAKTH's 
  CRCST, 
  MINEEALS 
  AND 
  EOCKS 
  119 
  

  

  lines 
  of 
  mountain 
  making 
  and 
  that 
  probably 
  the 
  outflows 
  of 
  

   molten 
  rock 
  are 
  due 
  to 
  local 
  relief 
  of 
  pressure 
  by 
  some 
  upward 
  

   movement 
  within 
  the 
  mountain 
  masses. 
  

  

  Envelopes 
  of 
  the 
  Earth 
  

  

  The 
  earth, 
  besides 
  possessing 
  a 
  solid 
  crust 
  and 
  an 
  intensely 
  

   heated 
  interior, 
  has 
  two 
  fluid 
  envelopes. 
  

  

  The 
  gaseous 
  envelope 
  or 
  atmosphere, 
  which 
  consists 
  of 
  the 
  air 
  

   we 
  breathe, 
  surrounds 
  the 
  entire 
  globe. 
  

  

  The 
  liquid 
  envelope, 
  of 
  which 
  the 
  various 
  portions 
  are 
  known 
  

   as 
  oceans, 
  seas, 
  gulfs, 
  bays, 
  lakes, 
  etc., 
  envelops 
  the 
  globe 
  only 
  

   in 
  part, 
  the 
  exposed 
  portions 
  of 
  dry 
  land 
  being 
  known 
  as 
  islands 
  

   and 
  continents. 
  

  

  These 
  two 
  envelopes, 
  under 
  the 
  influence 
  of 
  physical 
  forces, 
  are 
  

   very 
  active 
  agents 
  of 
  destruction, 
  transportation 
  and 
  deposition 
  

   in 
  their 
  action 
  on 
  the 
  earth's 
  crust. 
  

  

  The 
  present 
  relations 
  of 
  the 
  envelopes 
  to 
  the 
  continents, 
  the 
  

   forms 
  of 
  the 
  latter, 
  the 
  causes 
  of 
  climate, 
  the 
  origin 
  of 
  the 
  winds 
  

   and 
  ocean 
  currents 
  are 
  usually 
  discussed 
  under 
  the 
  head 
  of 
  

   physical 
  geography. 
  As 
  this 
  subject 
  is 
  not 
  at 
  present 
  illustrated 
  

   in 
  the 
  State 
  Museum, 
  the 
  student 
  is 
  referred 
  to 
  the 
  many 
  excel- 
  

   lent 
  text-books 
  on 
  this 
  science. 
  

  

  COMPONENTS 
  OF 
  THE 
  EARTH'S 
  CRUST, 
  MINERALS 
  

  

  AND 
  ROCKS 
  

  

  The 
  earth's 
  crust 
  consists 
  of 
  aggregates 
  of 
  matter 
  which 
  occur 
  

   in 
  stratified 
  and 
  unstratified 
  masses 
  and 
  are 
  known 
  as 
  rocks. 
  

   The 
  chemical 
  combinations 
  which 
  form 
  these 
  rocks 
  either 
  singly 
  

   or 
  in 
  mixture 
  are 
  called 
  minerals. 
  The 
  minerals, 
  therefore, 
  all 
  

   possess 
  a 
  definite 
  chemical 
  composition 
  which 
  can 
  be 
  expressed 
  

   by 
  formulae. 
  Kocks 
  vary 
  in 
  composition, 
  as 
  they 
  consist 
  of 
  one 
  

   or 
  more 
  minerals. 
  The 
  rocks 
  which 
  are 
  mixtures 
  of 
  several 
  min- 
  

   erals 
  vary 
  in 
  composition 
  as 
  the 
  proportions 
  of 
  their 
  components 
  

   vary; 
  and 
  it 
  is 
  possible 
  for 
  specimens 
  taken 
  from 
  the 
  same 
  rock 
  

   mass 
  to 
  differ 
  in 
  chemical 
  composition. 
  

  

  