﻿108 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  small 
  irregular 
  patches, 
  which 
  have 
  neither 
  the 
  crystallization 
  

   nor 
  the 
  cleavage 
  of 
  hornblende, 
  more 
  nearly 
  resembling 
  stains 
  

   of 
  oxide 
  of 
  iron. 
  It 
  is 
  to 
  these 
  that 
  the 
  yellowish 
  tint 
  of 
  the 
  

   matrix, 
  in 
  which 
  the 
  dark 
  crystalline 
  masses 
  are 
  imbedded, 
  is 
  

   due. 
  

  

  68. 
  Broadly-foliated 
  dark-green 
  diallage 
  sliced 
  and 
  ground 
  

   parallel 
  to 
  the 
  laminae. 
  The 
  most 
  striking 
  characteristic 
  is 
  the 
  

   striation 
  with 
  fine 
  lines, 
  giving 
  a 
  fibrous 
  appearance. 
  It 
  con- 
  

   tains 
  also 
  some 
  particles 
  of 
  quartz 
  and 
  magnetite. 
  

  

  69. 
  Hypersthene 
  occurring 
  in 
  the 
  labradorite 
  from 
  the 
  sum- 
  

   mit 
  of 
  Mt. 
  Marcy. 
  It 
  is 
  made 
  up 
  of 
  plates 
  or 
  flat, 
  short 
  rhom- 
  

   boidal 
  masses, 
  yellowish-red 
  to 
  opaque. 
  They 
  are 
  very 
  minute, 
  

   with 
  equally 
  small 
  intervals 
  between 
  them, 
  and 
  are 
  arranged 
  in 
  

   parallel 
  lines. 
  They 
  are 
  spread 
  through 
  a 
  transparent 
  matrix, 
  

   which 
  does 
  not 
  present 
  the 
  highly 
  twinned 
  appearance 
  of 
  the 
  

   labradorite 
  occurring 
  in 
  the 
  other 
  specimens 
  examined, 
  but 
  

   polarizing 
  magnificently 
  in 
  broad 
  bands 
  of 
  color 
  graduating 
  

   one 
  into 
  another 
  and 
  penetrated 
  by 
  quartz. 
  It 
  is 
  probably 
  

   plagioclase, 
  which 
  has 
  sliced 
  along 
  a 
  section 
  nearly 
  parallel 
  

   with 
  the 
  brachypinakoid. 
  

  

  V, 
  General 
  Conclusions. 
  

  

  I. 
  That 
  the 
  rocks 
  of 
  Essex 
  county 
  are 
  parts 
  of 
  the 
  Norian 
  

   System, 
  and 
  are 
  composed 
  of 
  Norites 
  similar 
  to 
  those 
  forming 
  

   the 
  rock-masses 
  of 
  the 
  same 
  system 
  in 
  Canada, 
  the 
  western 
  

   part 
  of 
  Scotland, 
  Norway 
  and 
  elsewhere. 
  

  

  II. 
  That 
  these 
  norites 
  are 
  a 
  stratified 
  rock, 
  but 
  have 
  under- 
  

   gone 
  a 
  metamorphosis 
  so 
  profound, 
  as 
  to 
  have 
  caused 
  them 
  

   to 
  be 
  regarded 
  by 
  Prof. 
  Emmons 
  and 
  earlier 
  observers, 
  as 
  

   unstratified. 
  The 
  dolerites, 
  which 
  are 
  formed 
  of 
  the 
  same 
  con- 
  

   stituent 
  minerals 
  and 
  are 
  of 
  the 
  mean 
  specific 
  gravity 
  of 
  these 
  

   norites, 
  have 
  probably 
  been 
  formed 
  from 
  a 
  portion 
  of 
  these 
  

   stratified 
  deposits 
  by 
  deeply 
  seated 
  metamorphic 
  action, 
  and 
  

   have 
  further 
  modified 
  and 
  greatly 
  tilted 
  the 
  superposed 
  rocks 
  

   in 
  the 
  course 
  of 
  their 
  extrusion. 
  

  

  III. 
  These 
  norites 
  are 
  marked 
  by 
  the 
  paucity 
  of 
  silica. 
  The 
  

   hypersthenes 
  and 
  diallages, 
  which 
  mainly 
  compose 
  the 
  pyrox- 
  

   enic 
  portions, 
  are 
  bisilicates 
  in 
  which 
  the 
  deficiency 
  of 
  silica 
  is 
  

   replaced 
  by 
  alumina. 
  The 
  labradorites 
  are 
  composed 
  chiefly 
  

   of 
  anorthite, 
  and 
  while 
  uncombined 
  silicic 
  acid 
  is 
  in 
  every 
  case 
  

  

  