﻿I58 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  mens, 
  the 
  microscope 
  reveals 
  the 
  presence 
  of 
  augite 
  and 
  hyper- 
  

   sthene 
  in 
  small 
  amounts 
  and 
  usually 
  some 
  magnetite 
  or 
  ilmenite. 
  

   In 
  portions 
  of 
  the 
  mass 
  that 
  show 
  effects 
  of 
  crushing 
  in 
  the 
  breaking 
  

   down 
  or 
  mashing 
  of 
  the 
  feldspar, 
  there 
  is 
  found 
  a 
  development 
  

   of 
  secondary 
  minerals 
  such 
  as 
  garnet, 
  biotite 
  and 
  calcite. 
  The 
  

   garnet 
  has 
  a 
  tendency 
  to 
  form 
  aggregates 
  about 
  the 
  magnetite, 
  

   which 
  owing 
  to 
  their 
  red 
  color 
  stand 
  out 
  plainly 
  from 
  their 
  sur- 
  

   roundings. 
  The 
  mineral 
  has 
  drawn 
  upon 
  the 
  magnetite 
  for 
  the 
  

   iron 
  and 
  the 
  feldspar 
  for 
  the 
  lime 
  and 
  silica 
  necessary 
  to 
  its 
  growth. 
  

   Biotite 
  is 
  not 
  so 
  common 
  as 
  the 
  garnet 
  with 
  which 
  it 
  is 
  closely 
  

   associated 
  and 
  no 
  doubt 
  genetically 
  related. 
  The 
  following 
  analysis, 
  

   quoted 
  from 
  a 
  paper 
  by 
  Prof. 
  Albert 
  R. 
  Leeds, 
  will 
  serve 
  to 
  

   show 
  the 
  chemical 
  character 
  of 
  the 
  anorthosite. 
  The 
  sample 
  from 
  

   which 
  it 
  was 
  made 
  was 
  taken 
  from 
  the 
  summit 
  of 
  Mt 
  Marcy. 
  

  

  SiO, 
  

   A1 
  2 
  C 
  

   Pe,0 
  3 
  . 
  

  

  FeO.. 
  

  

  A1 
  2 
  3 
  

  

  54 
  

  

  •47 
  

  

  26 
  

  

  •45 
  

  

  1 
  

  

  3 
  

  

  

  66 
  

  

  10. 
  

  

  80 
  

  

  

  69 
  

  

  

  92 
  

  

  4 
  

  

  37 
  

  

  

  53 
  

  

  CaO 
  

  

  MgO 
  

  

  k 
  2 
  o 
  : 
  

  

  Na 
  2 
  4 
  

  

  HO 
  

  

  100. 
  19 
  

  

  In 
  places 
  the 
  typical 
  anorthosite, 
  as 
  above 
  described, 
  gives 
  way 
  

   to 
  a 
  much 
  finer 
  grained 
  rock 
  in 
  which 
  the 
  pyroxene 
  minerals 
  are 
  

   more 
  prominent, 
  showing 
  a 
  transition 
  to 
  gabbro. 
  With 
  this 
  

   mineralogic 
  change 
  the 
  feldspar 
  individuals 
  decrease 
  in 
  size 
  and 
  

   number 
  and 
  the 
  color 
  becomes 
  greenish. 
  Such 
  phases 
  are 
  apt 
  to 
  

   have 
  a 
  gneissoid 
  texture 
  as 
  they 
  are 
  less 
  resistant 
  to 
  metamorphic 
  

   influences 
  than 
  the 
  anorthosite, 
  a 
  feature 
  that 
  is 
  illustrated 
  as 
  well 
  

   by 
  the 
  development 
  of 
  hornblende 
  in 
  the 
  place 
  of 
  the 
  pyroxene 
  

   minerals 
  and 
  of 
  abundant 
  garnet. 
  They 
  are 
  undoubtedly 
  a 
  differen- 
  

   tial 
  product 
  of 
  the 
  anorthosite, 
  but 
  it 
  is 
  not 
  always 
  clear 
  whether 
  

   the 
  gabbro 
  has 
  separated 
  in 
  place 
  or 
  has 
  come 
  up 
  through 
  the 
  

   anorthosite 
  in 
  the 
  form 
  of 
  dikes. 
  

  

  Ore 
  bodies. 
  Ore 
  is 
  found 
  in 
  both 
  the 
  anorthosite 
  and 
  the 
  gabbro. 
  

   The 
  anorthosite 
  is 
  the 
  commoner 
  wall 
  rock 
  and 
  the 
  ore 
  bodies 
  

   which 
  it 
  incloses 
  have 
  perhaps 
  the 
  greater 
  possibilities 
  for 
  commer- 
  

   cial 
  utilization, 
  due 
  to 
  their 
  uniform 
  character 
  and 
  higher 
  average 
  of 
  

  

  