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  Phillips 
  — 
  Mineralogical 
  Structure 
  and 
  Chemical 
  

  

  Analyses 
  lY 
  to 
  VI 
  of 
  Mesozoic 
  trap 
  are 
  given 
  for 
  conipari- 
  

   son 
  ; 
  lY 
  is 
  an 
  analysis 
  of 
  Rocky 
  Hill 
  trap, 
  by 
  G. 
  H. 
  Cook 
  ; 
  Y, 
  

   by 
  F. 
  A. 
  Gen 
  th, 
  'from 
  York 
  Co., 
  Pa.; 
  YI, 
  Trap 
  rock 
  at 
  

   Meriden, 
  Conn.,, 
  by 
  J. 
  H. 
  Pratt.'' 
  

  

  Analyses 
  Y 
  and 
  YI 
  represent 
  the 
  average 
  composition 
  of 
  

   the 
  Mesozoic 
  trap 
  of 
  the 
  Atlantic 
  coast, 
  and 
  by 
  a 
  comparison 
  

   with 
  tliese 
  analyses, 
  the 
  variation 
  of 
  the 
  Rocky 
  Hill 
  trap 
  from 
  

   the 
  mean 
  will 
  be 
  apparent. 
  The 
  most 
  important 
  points 
  to 
  be 
  

   noted 
  are 
  : 
  first, 
  that 
  the 
  Rocky 
  Hill 
  trap 
  is 
  high 
  in 
  alkalis 
  

   and 
  especially 
  so 
  in 
  potassium, 
  which 
  also 
  becomes 
  concentrated 
  

   locally 
  in 
  quarry 
  No. 
  3. 
  This 
  high 
  percentage 
  of 
  alkali 
  is 
  a 
  

   factor 
  which 
  exercises 
  an 
  important 
  influence 
  in 
  the 
  composi- 
  

   tion 
  and 
  formation 
  of 
  the 
  various 
  feldspars. 
  

  

  Second, 
  the 
  percentage 
  of 
  iron 
  is 
  high, 
  especially 
  the 
  fer- 
  

   rous 
  iron. 
  The 
  iron 
  as 
  well 
  shows 
  a 
  decided 
  concentration 
  in 
  

   No. 
  3. 
  This 
  high 
  amount 
  of 
  ferrous 
  iron 
  produces 
  a 
  diallage 
  

   remarkably 
  high 
  in 
  FeO, 
  as 
  the 
  analyses 
  will 
  show. 
  While 
  

   the 
  TiO^ 
  is 
  very 
  high 
  in 
  comparison 
  with 
  the 
  two 
  analyses 
  

   given, 
  there 
  are 
  other 
  analyses 
  in 
  which 
  TiO^ 
  is 
  present 
  in 
  

   equally 
  as 
  high 
  percentages. 
  In 
  the 
  West 
  Rock, 
  New 
  Haven, 
  

   there 
  is 
  1-4 
  L 
  per 
  cent 
  of 
  TiO^.'" 
  

  

  In 
  the 
  separation 
  of 
  the 
  various 
  mineral 
  components 
  for 
  

   analysis, 
  the 
  magnetite 
  was 
  taken 
  out 
  with 
  a 
  small 
  electro- 
  

   magnet, 
  the 
  strength 
  of 
  which 
  was 
  not 
  sufficient 
  to 
  attract 
  the 
  

   diallage 
  ; 
  though 
  diallage 
  in 
  which 
  magnetic 
  granules 
  had 
  

   developed 
  as 
  a 
  result 
  of 
  decomposition 
  and 
  oxidization 
  of 
  the 
  

   ferrous 
  iron 
  was 
  removed. 
  After 
  the 
  magnetic 
  portions 
  were 
  

   removed, 
  the 
  remainder 
  was 
  separated 
  with 
  the 
  Thoulet 
  solu- 
  

   tion. 
  The 
  diallagic 
  augite 
  separated 
  at 
  the 
  highest 
  specific 
  

   gravity 
  of 
  the 
  solution; 
  after 
  this 
  trials 
  were 
  made 
  at 
  various 
  

   stages 
  of 
  dilution, 
  until 
  the 
  specific 
  gravity 
  of 
  the 
  feldspars 
  

   was 
  reached. 
  Up 
  to 
  this 
  point 
  very 
  little 
  material 
  could 
  be 
  

   separated, 
  and 
  this, 
  when 
  examined 
  with 
  the 
  microscope, 
  was 
  

   found 
  not 
  to 
  be 
  homogeneous. 
  

  

  Neither 
  in 
  specimens 
  from 
  No. 
  2, 
  or 
  from 
  No. 
  3, 
  was 
  the 
  

   amount 
  separated 
  above 
  the 
  specific 
  gravity 
  of 
  2*72, 
  that 
  is 
  

   after 
  magnetite 
  and 
  diallage 
  had 
  been 
  removed, 
  very 
  large. 
  

   In 
  the 
  further 
  separation 
  of 
  the 
  feldspars, 
  the 
  solution 
  was 
  

   diluted 
  to 
  a 
  specific 
  gravity 
  of 
  2-69, 
  the 
  theoretical 
  density 
  

   which 
  would 
  separate 
  the 
  two 
  species 
  of 
  feldspars, 
  labradorite 
  

   on 
  the 
  one 
  side, 
  and 
  andesine 
  on 
  the 
  other'' 
  ; 
  then 
  again 
  

   diluted 
  to 
  a 
  density 
  of 
  2*60, 
  separating 
  the 
  anorthoclase 
  from 
  

   albite. 
  In 
  order 
  to 
  obtain 
  as 
  pure 
  sample 
  as 
  possible 
  of 
  each, 
  

   for 
  analysis, 
  each 
  specimen 
  was 
  put 
  through 
  the 
  solution 
  several 
  

   times. 
  While 
  the 
  specific 
  gravities 
  of 
  the 
  feldspars 
  overlap 
  

   each 
  other 
  to 
  a 
  great 
  extent, 
  still 
  tliese 
  portions 
  separated 
  will 
  

   give 
  an 
  idea 
  of 
  their 
  molecular 
  variation 
  in 
  different 
  positions 
  

  

  