﻿80 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  because, 
  as 
  he 
  states, 
  the 
  hypersthene 
  rock 
  and 
  its 
  varieties, 
  

   had 
  not 
  been 
  regarded 
  as 
  an 
  American 
  rock, 
  until 
  after 
  the 
  sur- 
  

   vey 
  of 
  New 
  York 
  was 
  in 
  progress. 
  In 
  using 
  the 
  term 
  Hyper- 
  

   sthene 
  Rock, 
  he 
  follows 
  MacCulloch, 
  who 
  had 
  previously 
  

   applied 
  this 
  name, 
  he 
  says, 
  to 
  the 
  same 
  mass 
  in 
  Scotland. 
  His 
  

   classification 
  of 
  the 
  varieties 
  of 
  hypersthene 
  rock 
  is 
  as 
  follows 
  : 
  

  

  1. 
  The 
  most 
  common 
  of 
  the 
  varieties 
  is 
  composed 
  wholly 
  of 
  

   labradorite, 
  though 
  to 
  the 
  eye 
  it 
  appears 
  like 
  a 
  mixed 
  or 
  com- 
  

   pound 
  mass, 
  as 
  it 
  has 
  the 
  aspect 
  of 
  being 
  made 
  up 
  of 
  two 
  

   distinct 
  minerals. 
  

  

  2. 
  Labradorite 
  and 
  hornblende. 
  The 
  hornblende 
  appears 
  

   usually 
  to 
  take 
  the 
  place 
  of 
  the 
  hypersthene, 
  though 
  not 
  always 
  ; 
  

   for 
  sometimes 
  the 
  latter 
  is 
  still 
  present. 
  

  

  3. 
  Labradorite, 
  hornblende 
  and 
  epidote 
  ; 
  the 
  latter, 
  however, 
  

   never 
  is 
  in 
  sufficient 
  quantity 
  to 
  give 
  character 
  to 
  the 
  rock. 
  

  

  4. 
  Granular 
  labradorite 
  and 
  mica, 
  a 
  variety 
  which 
  is 
  quite 
  

   dark, 
  and 
  has 
  much 
  the 
  aspect 
  of 
  trap. 
  

  

  In 
  this 
  classification 
  the 
  variety 
  composed 
  of 
  labradorite 
  and 
  

   hypersthene, 
  from 
  which 
  the 
  whole 
  formation 
  derives 
  its 
  name, 
  

   has 
  been 
  accidentally 
  omitted. 
  

  

  To 
  this 
  should 
  be 
  added 
  as 
  distinguishing 
  characteristics 
  : 
  

  

  5. 
  That 
  magnetic 
  oxide 
  is 
  also 
  disseminated 
  very 
  frequently 
  

   through 
  the 
  mass, 
  making 
  it 
  eminently 
  an 
  iron 
  -bearing 
  rock 
  ; 
  

   also 
  garnet 
  in 
  grains, 
  or 
  small 
  masses, 
  scarcely 
  ever 
  in 
  crystals 
  ; 
  

   it 
  is 
  common 
  near 
  the 
  junction 
  of 
  the 
  rock 
  with 
  the 
  ore 
  beds. 
  

  

  The 
  rock 
  has 
  a 
  jointed 
  structure 
  ; 
  in 
  addition 
  to 
  which, 
  it 
  is 
  

   often 
  traversed 
  by 
  segregated 
  veins 
  and 
  cracks 
  or 
  false 
  joints 
  ; 
  

   the 
  latter 
  serving 
  to 
  divide 
  the 
  mass 
  into 
  wedge-form 
  pieces, 
  

   are 
  finally 
  detached, 
  and 
  form 
  the 
  talus 
  at 
  the 
  base 
  of 
  the 
  cliffs. 
  

  

  The 
  predominant 
  color 
  of 
  the 
  rock 
  is 
  smoke-grey, 
  light 
  or 
  

   dark, 
  weathering 
  to 
  ash-grey. 
  The 
  color 
  most 
  constantly 
  asso- 
  

   ciated 
  with 
  this 
  is 
  a 
  dingy-green, 
  which 
  belongs, 
  according 
  to 
  

   Emmons, 
  to 
  the 
  labradorite, 
  and 
  not 
  to 
  the 
  other 
  minerals 
  

   which 
  happen 
  to 
  be 
  present. 
  It 
  is 
  traversed 
  by 
  a 
  double 
  sys- 
  

   tem 
  of 
  joints, 
  or 
  divisional 
  seams, 
  which 
  run 
  S. 
  5° 
  W. 
  and 
  N. 
  

   85° 
  E., 
  with 
  a 
  variation 
  in 
  this 
  direction, 
  amounting 
  to 
  from 
  5° 
  to 
  

   10°, 
  when 
  observed 
  at 
  different 
  places. 
  Quartz 
  is 
  seldom 
  found 
  

   in 
  this 
  rock, 
  occurring 
  only 
  in 
  seams 
  or 
  thin 
  irregular 
  veins. 
  

   The 
  associated 
  rocks 
  are 
  those 
  allied 
  to 
  trap, 
  of 
  which 
  the 
  most 
  

   constant 
  in 
  its 
  occurrence 
  is 
  a 
  compound 
  of 
  hornblende 
  and 
  

  

  