﻿Composition 
  of 
  the 
  Trap 
  of 
  Rocky 
  Hill, 
  W. 
  J. 
  279 
  

  

  Chemical 
  Analysis. 
  

  

  In 
  the 
  analysis 
  of 
  the 
  rock, 
  what 
  seemed 
  to 
  be 
  typical 
  speci- 
  

   mens 
  from 
  quarries 
  Eo. 
  3 
  and 
  No. 
  2, 
  and 
  a 
  specimen 
  from 
  the 
  

   microcrystalline 
  contact 
  region, 
  were 
  selected. 
  These 
  three 
  

   specimens, 
  it 
  was 
  thought, 
  w^ould 
  represent 
  the 
  three 
  stages 
  in 
  

   the 
  trap 
  so 
  decidedly 
  different 
  in 
  the 
  development 
  of 
  its 
  crys- 
  

   tals, 
  and 
  would 
  also 
  give 
  a 
  good 
  basis, 
  by 
  means 
  of 
  which 
  the 
  

   magmas 
  from 
  out 
  of 
  which 
  they 
  were 
  crystallized 
  might 
  be 
  

   compared. 
  The 
  sijecimen 
  from 
  the 
  border 
  was 
  taken, 
  as 
  the 
  

   magma 
  must 
  have 
  consolidated 
  upon 
  contact 
  with 
  the 
  sedi- 
  

   mentary 
  rock, 
  or 
  at 
  least 
  soon 
  after 
  injection 
  between 
  the 
  

   strata, 
  and 
  can 
  therefore 
  be 
  held 
  to 
  represent 
  the 
  composition 
  

   of 
  the 
  entire 
  mass 
  at 
  tlie 
  time 
  of 
  its 
  intrusion, 
  or 
  its 
  original 
  

   composition. 
  

  

  In 
  specific 
  gravity 
  these 
  specimens 
  fall 
  in 
  the 
  middle 
  of 
  the 
  

   series 
  observed 
  in 
  the 
  Mesozoic 
  trap. 
  The 
  average 
  for 
  the 
  

   entire 
  dike 
  would 
  be 
  about 
  3. 
  The 
  densities 
  of 
  specimens 
  col- 
  

   lected 
  at 
  various 
  localities 
  along 
  the 
  ridge 
  vary 
  between 
  3*125, 
  

   the 
  density 
  of 
  a 
  specimen 
  from 
  the 
  Hopewell 
  extremity, 
  and 
  

   2 
  '935, 
  the 
  density 
  of 
  one 
  taken 
  near 
  the 
  village 
  of 
  Rocky 
  

   Hill. 
  The 
  density 
  of 
  the 
  typical 
  rock 
  from 
  quarry 
  No. 
  2 
  was 
  

   found 
  to 
  be 
  2-968 
  ; 
  that 
  of 
  quarry 
  No. 
  3, 
  3-023. 
  These 
  varia- 
  

   tions 
  in 
  density 
  are 
  no 
  more 
  than 
  would 
  be 
  expected, 
  caused 
  

   by 
  the 
  local 
  change, 
  both 
  in 
  the 
  composition 
  and 
  relative 
  pro- 
  

   portion 
  of 
  its 
  primary 
  minerals. 
  

  

  Analyses 
  of 
  the 
  Rocky 
  Hill 
  Trap. 
  

  

  I. 
  II. 
  III. 
  IV. 
  V. 
  YI. 
  

  

  Quarry 
  Quarry 
  Contact 
  

  

  No. 
  3. 
  No. 
  2. 
  band. 
  

  

  SiO, 
  56-78 
  50-34 
  51-46 
  52 
  1 
  52-53 
  52-37 
  

  

  'J'iO^ 
  -- 
  1-44 
  1-56 
  1-06 
  -32 
  -21 
  

  

  Al^Oj 
  14-33 
  15-23 
  13-98 
  16-7 
  14-35 
  15-06 
  

  

  IXO3 
  5-76 
  2-82 
  2-66 
  5-93 
  2-34 
  

  

  FeO 
  9-27 
  11-17 
  8*92 
  12-7 
  5-45 
  9-82 
  

  

  MnO 
  -25 
  -14 
  trace 
  -32 
  

  

  CaO 
  . 
  5-26 
  9 
  61 
  10*49 
  10-8 
  10'27 
  7-33 
  

  

  MgO 
  1-58 
  5-81 
  7-59 
  3-2 
  7'99 
  5-38 
  

  

  NaO. 
  3-43 
  2-93 
  ) 
  , 
  ^^ 
  2*3 
  1*87 
  4*04 
  

  

  K,0 
  1-75 
  1-02 
  j" 
  '^ 
  -8 
  -97 
  -92 
  

  

  P,0^... 
  -36 
  -20 
  -17 
  -15 
  

  

  S03= 
  .08 
  

   H,0 
  above 
  110° 
  -10 
  -07 
  * 
  1-4 
  ignition 
  1-23 
  2-24 
  

   H^ObelowllO° 
  -33 
  '19 
  

  

  100-64 
  101-09 
  101-08 
  100" 
  10M4 
  100-03 
  

  

  * 
  IJDfortunately 
  for 
  direct 
  comparison 
  this 
  specimen 
  was 
  dried 
  at 
  150° 
  before 
  

   it 
  was 
  analyzed, 
  but 
  the 
  percentage 
  of 
  H2O 
  must 
  have 
  been 
  small. 
  

  

  