HIGHLANDS    OF    NEW    JERSEY.  643 
The  granite  occurring  in  the  area  is  intrusive  in  the  white  lime- 
stone, and  the  nature  of  the  contacts  of  the  granite  and  the  Cambrian 
quartzite  indicates  that  the  intrusion  was  prior  to  the  deposition  of 
the  Cambrian  quartzite  and  the  blue  limestone.  While  the  intrusion 
of  the  granite  has  caused  local  metamorphism  of  the  white  limestone, 
it  is  believed  that  the  crystallization  of  the  limestone  antedated  the 
granitic  intrusion  and  was  contemporaneous  with  the  crystallization 
of  the  gneisses  in  their  present  form. 
The  structural  relations  of  the  three  belts  of  Cambrian  blue  lime- 
stone with  the  gneiss  and  the  white  limestone  are  such  as  to  indicate 
unconformity.  Along  the  normal  contacts  of  the  blue  and  the  white 
limestones  the  quartzite  intervenes  between  the  two.  The  bedding 
of  the  blue  limestone  and  the  underlying  quartzite  is  everywhere  con- 
formable, while  the  dip  of  the  foliation  of  the  white  limestone  and  the 
gneisses  is  discordant  with  this  bedding. 
Isolated  patches  of  Cambrian  quartzite  are  found  within  the  white 
limestone  area.  In  one  place  a  crevice  in  the  white  limestone  is  filled 
with  the  Cambrian  quartzite  containing  undoubted  pebbles  of  the 
white  limestone. 
Spencer,110  in  1904,  regards  the  crystalline  rocks  of  the  New  Jersey 
Highlands,  excepting  the  white  limestone,  as  intrusive.  He  believes 
their  gneissic  structure  an  original  feature  of  their  first  consolidation, 
and  not  due  to  metamorphism.  In  Sussex  County  there  are  several 
fairly  distinct  types  of  crystalline  rock,  all  of  which  are  stated  to  be 
intrusive  with  respect  to  the  white  limestone,  though  among  them- 
selves the  relations  are  often  indeterminate.  The  reason  for  this 
seems  to  be  that  the  different  rocks  became  mixed  or  interlarded  while 
still  in  a  noncrystalline  or  magmatic  condition.  Three  types  of 
gneissoid  rock  are  separated  on  the  basis  of  color  and  mineral  com- 
position. In  different  places  two  of  these  types  are  found  intrusive 
into  the  white  limestone,  while  the  third,  a  white  rock  characterized 
by  oligoclase,  is  also  evidently  later  than  the  limestone,  since  it  cuts 
one  of  the  others.  Pegmatite  occurs  in  large  and  small  masses  in- 
closed in  all  of  the  other  crystalline  formations.  Grains  of  magnetite 
occur  in  all  of  the  igneous  rocks,  and  shoots  of  ore  arc  inclosed  by  all 
of  them  and  also  by  the  limestone;  but  pegmatite  is  always  encoun- 
tered in  greater  or  less  amounts  wherever  there  is  any  large  amount  of 
magnetite.  It  is  concluded  that  the  masses  of  magnetite  were  segre- 
gated during  the  invasion  of  the  pegmatite  dikes. 
Spencer,117  in  1905,  considers  all  the  well-marked  types  of  gneiss 
occurring  in  the  Franklin  Furnace  quadrangle  as  of  igneous  origin. 
The  pre-Cambrian  rocks  are  grouped  under  five  head-:  |  1  )  The  white 
limestone;  (2)  a  complex  of  light-gray  and  dark-gray  gneiss;  (3) 
black  hornblende  and  pyroxene  gneiss;  (1)  white  granite  gneiss; 
and  (5)  pegmatite.    This  order  represents  the  general  age  relations, 
