﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  85 
  

  

  large 
  proportion 
  in 
  a 
  gaugue 
  of 
  black 
  hornblende 
  with 
  a 
  little 
  feld- 
  

   spar, 
  in 
  Cornwall, 
  Orange 
  county. 
  Large 
  and 
  well-defined 
  prisms 
  

   of 
  zircon, 
  which 
  occur 
  with 
  apatite 
  and 
  feldspar 
  in 
  Hammond, 
  

   St. 
  Lawrence 
  county, 
  New 
  York, 
  are 
  sometimes, 
  like 
  the 
  iclocrase 
  

   noted 
  above, 
  skeleton 
  crystals, 
  filled 
  with 
  carbonate 
  of 
  lime 
  (Beck, 
  

   Mineralogy 
  of 
  New 
  York, 
  page 
  381). 
  

  

  Spinel. 
  — 
  This 
  mineral 
  is 
  often 
  abundant 
  in 
  the 
  calcareous 
  Lau- 
  

   rentian 
  veins, 
  generally 
  associated 
  with 
  chondrodite, 
  pyroxene, 
  

   clintonite, 
  serpentine, 
  ilmenite, 
  and 
  other 
  species. 
  Sometimes 
  it 
  

   is 
  imbedded 
  in 
  calcite 
  without 
  any 
  other 
  mineral, 
  as 
  in 
  Burgess, 
  

   where 
  a 
  mass 
  of 
  pink 
  limestone, 
  probably 
  a 
  veinstone, 
  has 
  afforded 
  

   fine 
  crystals 
  of 
  black 
  spinel 
  an 
  inch 
  in 
  diameter. 
  In 
  Ross, 
  similar 
  

   crystals 
  occur 
  in 
  a 
  calcite 
  vein 
  with 
  orthoclase, 
  fluor-spar 
  and 
  

   apatite 
  ; 
  grains 
  of 
  the 
  latter 
  mineral 
  are 
  frequently 
  imbedded 
  in 
  

   the 
  spinel 
  crystals. 
  Small 
  crystals 
  of 
  spinel 
  are 
  sometimes 
  found 
  

   disseminated 
  in 
  what 
  appear 
  to 
  be 
  stratified 
  limestones. 
  Although 
  

   the 
  spinel 
  of 
  the 
  Laurentian 
  limestones 
  is 
  generally 
  black, 
  blue, 
  

   red 
  and 
  green 
  varieties 
  are 
  occasionally 
  met 
  with. 
  The 
  dysluite 
  

   or 
  zinciferous 
  spinel 
  is 
  worthy 
  of 
  notice, 
  as 
  occurring 
  in 
  Stirling, 
  

   New 
  Jersey, 
  with 
  other 
  zinc-bearing 
  minerals. 
  

  

  Volknerite. 
  — 
  To 
  this 
  species, 
  a 
  hydrous 
  aluminate 
  of 
  magnesia, 
  

   Dana 
  has 
  referred 
  the 
  houghite 
  of 
  Shepard, 
  from 
  St. 
  Lawrence 
  

   county, 
  New 
  York, 
  which 
  occurs 
  associated 
  with 
  crystals 
  of 
  spinel, 
  

   and 
  having 
  the 
  same 
  octahedral 
  form, 
  but 
  distinguished 
  by 
  a 
  low 
  

   specific 
  gravity, 
  and 
  a 
  softness 
  like 
  steatite. 
  A 
  gradation 
  is 
  seen 
  

   from 
  the 
  hard 
  spinels 
  to 
  the 
  houghite 
  crystals, 
  which 
  still 
  include 
  

   a 
  portion 
  of 
  spinel, 
  but 
  consist 
  chiefly 
  of 
  a 
  matter 
  having 
  the 
  com- 
  

   position 
  of 
  volknerite. 
  It 
  would 
  seem 
  that 
  the 
  crystallogenic 
  force 
  

   of 
  the 
  spinel 
  has 
  given 
  its 
  form 
  to 
  accompanying 
  volknerite. 
  

   Small 
  steatitic 
  octahedrons, 
  apparently 
  similar 
  to 
  the 
  houghite, 
  

   have 
  been 
  found 
  imbedded 
  in 
  serpentine, 
  in 
  Burgess, 
  but 
  require 
  

   farther 
  examination. 
  The 
  hydro 
  talcite, 
  which 
  is 
  regarded 
  as 
  iden- 
  

   tical 
  with 
  volknerite, 
  occurs 
  with 
  ilmenite 
  in 
  the 
  Laurentian 
  serpen- 
  

   tine 
  of 
  Snarum, 
  in 
  Norway. 
  

  

  Corundum. 
  — 
  Crystallized 
  corundum, 
  white, 
  blue 
  or 
  red 
  in 
  color, 
  

   occurs 
  with 
  associations 
  similar 
  to 
  those 
  of 
  spinel, 
  which 
  occasion- 
  

   ally 
  accompanies 
  it. 
  Crystals 
  of 
  corundum 
  line 
  cavities 
  in 
  the 
  

   large 
  spinels 
  from 
  Orange 
  county, 
  New 
  York. 
  The 
  red 
  crystals 
  

   from 
  Vernon, 
  New 
  Jersey, 
  as 
  described 
  by 
  Blake, 
  like 
  the 
  idocrase 
  

  

  [Senate 
  No. 
  92.] 
  8 
  

  

  