﻿Phillijps 
  — 
  Miner 
  alog 
  iced 
  Structure, 
  etc. 
  267 
  

  

  Art. 
  XXX. 
  — 
  The 
  Mineralogical 
  Structure 
  and 
  Chemical 
  

   Composition 
  of 
  the 
  Trap 
  of 
  Bochy 
  Hill, 
  iK 
  J. 
  / 
  bj 
  Alex- 
  

   ander 
  Hamilton 
  Phillips, 
  D.Sc. 
  

  

  Introduction. 
  

  

  The 
  Mesozoic 
  trap 
  rocks, 
  or 
  trap 
  dikes 
  of 
  the 
  eastern 
  

   coast 
  of 
  the 
  United 
  States, 
  are 
  almost 
  entirely 
  confined 
  to 
  a 
  

   comparatively 
  narrow 
  strip 
  of 
  country, 
  in 
  which 
  the 
  Triassic 
  

   formation 
  appears 
  at 
  the 
  surface. 
  The 
  two 
  seem 
  to 
  be 
  so 
  con- 
  

   stantly 
  connected, 
  that 
  almost 
  every 
  isolated 
  Triassic 
  area, 
  

   however 
  small, 
  is 
  accompanied 
  with 
  its 
  corresponding 
  intrusions 
  

   of 
  trap. 
  

  

  The 
  Triassic 
  strata 
  of 
  the 
  Atlantic 
  coast 
  extend 
  in 
  a 
  north- 
  

   east 
  and 
  southwest 
  direction 
  from 
  Nova 
  Scotia 
  to 
  N'orth 
  Caro- 
  

   lina, 
  through 
  an 
  interrupted 
  course, 
  and 
  are 
  found 
  more 
  or 
  

   less 
  in 
  isolated 
  patches 
  along 
  the 
  western 
  portion 
  of 
  the 
  coastal- 
  

   plain, 
  and 
  lying 
  next 
  the 
  older 
  crystalline 
  schists 
  of 
  the 
  Appa- 
  

   lachian 
  range, 
  into 
  and 
  through 
  the 
  border 
  of 
  w^iich 
  the 
  trap 
  

   dikes 
  also 
  extend. 
  

  

  In 
  size, 
  these 
  dikes 
  vary 
  from 
  a 
  foot 
  or 
  so 
  in 
  thickness 
  to 
  

   such 
  large 
  masses 
  as 
  are 
  represented 
  by 
  the 
  Palisades 
  of 
  the 
  

   Hudson. 
  Their 
  direction, 
  especially 
  of 
  the 
  larger 
  masses, 
  con- 
  

   forms 
  in 
  a 
  marked 
  degree 
  to 
  the 
  strike 
  of 
  the 
  strata 
  in 
  which 
  

   they 
  lie, 
  and 
  owing 
  to 
  their 
  greater 
  power 
  of 
  resisting 
  erosion, 
  

   they 
  appear 
  on 
  the 
  surface 
  as 
  parallel 
  ridges, 
  which 
  mark 
  the 
  

   transition 
  from 
  the 
  low 
  level 
  country 
  of 
  the 
  coastal-plain 
  to 
  

   the 
  higher 
  foot-hills 
  of 
  the 
  Appalachian 
  Range. 
  

  

  Throughout 
  this 
  entire 
  area 
  of 
  some 
  twelve 
  hundred 
  miles 
  

   in 
  extent, 
  the 
  mineralogical 
  composition 
  of 
  the 
  trap 
  is 
  wonder- 
  

   fully 
  alike, 
  as 
  has 
  been 
  pointed 
  out 
  from 
  results 
  of 
  analyses 
  of 
  

   this 
  rock 
  from 
  localities 
  widely 
  separated.' 
  ^ 
  

  

  The 
  specific 
  gravity 
  of 
  these 
  traps 
  varies, 
  from 
  data 
  collected 
  

   by 
  J. 
  D. 
  Dana," 
  from 
  2'94:, 
  that 
  of 
  the 
  Palisades, 
  to 
  3-16, 
  that 
  

   of 
  a 
  specimen 
  from 
  North 
  Carolina 
  ; 
  while 
  there 
  are 
  cases 
  in 
  

   which 
  the 
  specific 
  gravity 
  falls 
  as 
  low 
  as 
  2"83.^ 
  3*16 
  still 
  seems 
  

   to 
  be 
  the 
  maximum. 
  

  

  The 
  mineralogical 
  constituents 
  were 
  generally 
  supposed 
  to 
  

   be 
  magnetite, 
  augite 
  and 
  labradorite. 
  (x. 
  W. 
  Hawes^ 
  was 
  the 
  

   first 
  to 
  show 
  the 
  complex 
  character 
  of 
  the 
  feldspars, 
  from 
  

   analyses 
  made 
  of 
  specimens 
  of 
  the 
  West 
  Pock, 
  at 
  New 
  Haven, 
  

   and 
  of 
  the 
  New 
  Jersey 
  Palisades. 
  Campbell 
  and 
  Brown 
  later 
  

   pointed 
  out 
  other 
  complexities 
  than 
  that 
  of 
  the 
  feldspars, 
  and 
  

   a 
  specimen 
  from 
  Milford, 
  N. 
  J., 
  is 
  described 
  as 
  a 
  liypersthene- 
  

   diabase^ 
  ; 
  as 
  well 
  as 
  an 
  olivine-diabase 
  from 
  Yirginia. 
  

  

  * 
  See 
  references 
  given 
  on 
  p. 
  285. 
  

  

  