﻿COM^OKENTS 
  OF 
  THE 
  EARTH's 
  CRUST, 
  MINERALS 
  AND 
  ROCKS 
  125 
  

  

  Orthoclase 
  and 
  

   hornblende 
  

  

  Plagfioclase 
  and. 
  

   hornblende 
  

  

  Piagioclase 
  and 
  

   augite 
  

  

  Piagioclase 
  

  

  and 
  

   hyperstbene 
  

  

  With 
  

   quartz 
  

  

  Without 
  

   quartz 
  

  

  With 
  

   quartz 
  

  

  Wilhout 
  

   quartz 
  

  

  With 
  

   olivine 
  

  

  Without 
  

   olivine 
  

  

  

  6ranit« 
  

  

  Quartz 
  

   porphyry 
  

   rhyolite 
  

  

  Syenite 
  

   Trachyte 
  

  

  Quartz 
  

   diorit© 
  

  

  Quartz 
  

   porphyrite 
  

  

  Plutonic 
  

   Diorite 
  

  

  Volcanic 
  

  

  Andesite 
  

   porphyrite 
  

  

  OliTine 
  

   diabase 
  

  

  Basalt 
  

  

  Diabase 
  

  

  Augite 
  

   andesite 
  

  

  Xorite 
  

  

  Hyporsthene 
  

   andesite 
  

  

  Sedimentary 
  rocks 
  

  

  These 
  are, 
  for 
  the 
  most 
  part, 
  deposited 
  in 
  water, 
  and 
  are 
  of 
  

   three 
  classes, 
  mechanical, 
  chemical 
  and 
  organic. 
  

   The 
  principal 
  examples 
  of 
  these 
  are: 
  

  

  r 
  1 
  Sand, 
  gravel, 
  sandstone 
  and 
  conglomerate. 
  These 
  

  

  I 
  are 
  the 
  debris 
  of 
  rocks 
  containing 
  quartz. 
  

  

  Mechanical 
  ^ 
  2 
  Clay 
  and 
  shale. 
  These 
  are 
  formed 
  of 
  the 
  debris 
  of 
  

   feldspar 
  and 
  the 
  residuum 
  from 
  impure 
  limestone. 
  

  

  3 
  Tujffs. 
  Deposits 
  of 
  loose 
  volcanic 
  materials. 
  

  

  1^4 
  Rock 
  salt 
  (chloride 
  of 
  sodium), 
  deposited 
  by 
  eva- 
  

  

  I 
  poration 
  from 
  bodies 
  of 
  salt 
  water. 
  

  

  Chemical 
  ^ 
  5 
  Gypsum 
  (sulphate 
  of 
  lime), 
  deposited 
  by 
  evapora- 
  

  

  I 
  tion 
  from 
  bodies 
  of 
  salt 
  water. 
  All 
  sea 
  water 
  

  

  V 
  contains 
  sulphate 
  of 
  lime. 
  

  

  f6 
  Limestone, 
  deposited 
  in 
  oceans 
  from 
  debris 
  of 
  

  

  I 
  marine 
  animals, 
  corals, 
  mollusks, 
  etc. 
  

  

  Organic 
  ^ 
  Coal, 
  formed 
  from 
  accumulations 
  of 
  vegetation 
  in 
  

  

  L 
  

  

  marshes. 
  

  

  MetamorpMc 
  rocks 
  

  

  These 
  have 
  been 
  subjected 
  to 
  heat 
  and 
  pressure 
  usually 
  in 
  the 
  

   presence 
  of 
  moisture, 
  and 
  have 
  lost 
  their 
  original 
  form 
  and 
  

   structure. 
  They 
  include 
  the 
  following: 
  

  

  Gneiss, 
  which 
  ordinarily 
  has 
  the 
  same 
  composition 
  as 
  granite,^ 
  

   with 
  a 
  foliated 
  or 
  schistose 
  structure. 
  

  

  a 
  In 
  modern 
  usage 
  the 
  word 
  gneiss 
  designates 
  only 
  the 
  schistose 
  or 
  foliated 
  

   Btructure 
  and 
  any 
  massive 
  rook 
  made 
  schistose 
  by 
  metamorphisni 
  is 
  called 
  gneiss. 
  

  

  