﻿268 
  Phillips 
  — 
  Mineralogieal 
  Structure 
  and 
  Chemical 
  

  

  Magnetite, 
  augite 
  and 
  labradorite 
  may 
  be 
  considered 
  as 
  the 
  

   most 
  widely 
  distributed 
  and 
  characteristic 
  minerals 
  of 
  the 
  

   Triassic 
  traps, 
  and, 
  from 
  the 
  constant 
  occurrence 
  of 
  small 
  per- 
  

   centages 
  of 
  P2O5 
  in 
  all 
  analyses, 
  apatite 
  might 
  be 
  added 
  to 
  

   these 
  three. 
  The 
  above 
  is, 
  however, 
  by 
  no 
  means 
  a 
  complete 
  

   list 
  of 
  primary 
  minerals 
  which 
  occur 
  locally, 
  for 
  added 
  to 
  these, 
  

   olivine, 
  anorthite, 
  hypersthene, 
  biotite, 
  pyrite, 
  and 
  zircon 
  are 
  

   local 
  minerals, 
  given 
  here 
  in 
  the 
  order 
  of 
  their 
  frequency. 
  

  

  The 
  minerals 
  of 
  contact 
  and 
  decomposition, 
  or 
  of 
  secondary 
  

   formation, 
  are 
  well 
  known 
  and 
  have 
  a 
  well 
  deserved 
  reputation 
  

   from 
  their 
  beauty 
  and 
  perfection 
  of 
  crystalline 
  form 
  ; 
  they 
  

   have 
  found 
  their 
  way 
  into 
  all 
  collections. 
  

  

  Description 
  of 
  the 
  Eocky 
  Hill 
  Dike, 
  and 
  its 
  relation 
  to 
  the 
  

   Sedimentary 
  Strata. 
  

  

  In 
  its 
  relation 
  to 
  the 
  sedimentary 
  strata, 
  the 
  Rocky 
  HiL 
  

   dike 
  is 
  no 
  exception 
  to 
  the 
  rule, 
  lying 
  well 
  up 
  in 
  the 
  strata, 
  

   which 
  represent 
  the 
  Triassic 
  beds, 
  and 
  especially 
  so 
  at 
  either 
  of 
  

   its 
  extremities. 
  

  

  The 
  Triassic 
  has 
  been 
  divided 
  here 
  into 
  three 
  divisions^ 
  : 
  

   the 
  Stockton, 
  Lockatong 
  and 
  Brunswick 
  shales 
  ; 
  the 
  Stockton 
  

   being 
  the 
  lower 
  and 
  older 
  in 
  the 
  series, 
  lying 
  just 
  above 
  the 
  

   crystalline 
  gneiss. 
  

  

  The 
  Rocky 
  Hill 
  trap 
  extends 
  for 
  some 
  fifteen 
  miles 
  in 
  a 
  

   northeast 
  and 
  southwest 
  direction 
  through 
  these 
  beds 
  of 
  shale, 
  

   lying 
  for 
  the 
  most 
  part 
  within 
  the 
  Brunswick 
  shales, 
  to 
  the 
  

   strike 
  of 
  which 
  it 
  seems 
  to 
  conform 
  for 
  about 
  six 
  miles 
  west 
  

   of 
  the 
  village 
  of 
  Rocky 
  Hill, 
  where 
  it 
  makes 
  a 
  slight 
  curve, 
  

   and 
  breaks 
  through 
  the 
  strata 
  extending 
  to 
  a 
  higher 
  horizon 
  in 
  

   the 
  Brunswick 
  shales 
  ; 
  at 
  this 
  bend 
  the 
  ridge 
  reaches 
  its 
  

   highest 
  elevation. 
  Mount 
  Rose 
  possessing 
  an 
  elevation 
  of 
  415 
  

   feet, 
  as 
  given 
  in 
  the 
  JN'ew 
  Jersey 
  Geological 
  Report. 
  From 
  

   this 
  point 
  it 
  gradually 
  declines 
  in 
  height 
  eastward, 
  until 
  the 
  

   ridge 
  entirely 
  disappears 
  at 
  the 
  country 
  level 
  east 
  of 
  the 
  Penn- 
  

   sylvania 
  railroad. 
  One 
  mile 
  east 
  of 
  Rocky 
  Hill 
  village 
  it 
  

   divides 
  into 
  two 
  branches 
  ; 
  one 
  extends 
  east, 
  the 
  other 
  north 
  

   towards 
  Griggstown, 
  this 
  branch 
  being 
  much 
  the 
  smaller 
  of 
  

   the 
  two 
  in 
  extent, 
  and 
  separated 
  from 
  the 
  easterly 
  one 
  by 
  a 
  

   formation 
  known 
  as 
  the 
  Sand 
  Hills. 
  Whether 
  these 
  two 
  

   branches 
  are 
  connected 
  by 
  a 
  sheet 
  of 
  trap 
  underlying 
  the 
  Sand 
  

   Hills 
  as 
  suggested 
  by 
  IN". 
  H. 
  Darton,' 
  produced 
  by 
  an 
  upward 
  

   folding 
  of 
  the 
  trap 
  is 
  difficult 
  to 
  prove, 
  although 
  from 
  con- 
  

   sideration 
  of 
  the 
  whole 
  lay 
  of 
  the 
  strata, 
  this 
  seems 
  very 
  

   probable. 
  

  

  The 
  surface 
  occupied 
  by 
  the 
  trap 
  is 
  thickly 
  strewn 
  with 
  

   large 
  irregular, 
  though 
  somewhat 
  rounded 
  masses 
  of 
  rock 
  in 
  

  

  