THE  GRIGGSTOWN,  N.  J.,  COPPER  DEPOSIT. 
By  Walter  Harvey  Weed. 
Throughout  the  Atlantic  States  the  red  sandstones  of  Triassic  age, 
grouped  as  the  Newark  formation,  contain  intruded  masses  of  trap 
(diabase)  which  form  the  eminences  rising  above  the  relatively  flat 
country  into  which  the  soft  sandstones  have  been  eroded.  Copper 
ores  occur  at  various  localities  throughout  this  entire  region,  and 
always  near  the  trap  rocks.  Attempts  to  work  these  deposits  have 
been  made  in  various  States,  and  in  the  early  part  of  the  last  centuiy, 
when  the  price  of  copper  was  high,  a  considerable  amount  was  obtained 
from  the  deposits  of  this  type  in  New  Jerse}7.  The  deposits  in  that 
State  are  typical  of  those  of  the  class,  and  as  they  have  been  exposed 
by  extensive  underground  workings  they  are  best  fitted  for  careful 
investigation.  In  Bulletin  213  a  summary  was  given  of  the  results  of 
a  study  of  the  deposits  found  beneath  the  great  trap  sheet  of  Watch- 
ung  or  Orange  Mountain,  New  Jersey,  particularly  of  the  deposit 
near  Somerville.  The  held  evidence  shows  conclusively  that  this 
great  trap  mass  was  a  lava  flow  practically  contemporaneous  with  the 
red  sandstones  that  lie  above  and  below  it.  There  is,  therefore,  no 
thermal  metamorphism  of  the  rocks,  and  no  possible  derivation  of  the 
copper  from  direct  igneous  emanations  from  this  trap  rock. 
In  November,  1903,  a  brief  trip  was  paid  to  another  New  Jersey 
property,  formerly  worked  for  copper,  in  which  the  ores  do  not  occur 
in  immediate  contact  with  trap  rock,  but  in  the  sedimentary  rocks 
lying  above  an  intrusive  sheet  of  trap  whose  heat  has  baked  and  altered 
the  soft,  red  shales  to  a  hard,  compact  hornstone.  This  property  is 
alluded  to  in  all  geological  reports  as  the  Griggstown  copper  mine, 
and  this  name  is  therefore  retained.  The  following  notes  are  pre- 
sented in  advance  of  the  detailed  study  to  be  included  as  part  of  a 
general  report  on  the  copper  deposits  of  the  Appalachian  States. 
Location. — The  property  is  located  in  the  hilly  tract  north  of 
Princeton,  N.  J.,  and  about  8  miles  from  that  town.  It  is  nearer  the 
town  of  Rocky  Hill,  the  terminus  of  a  branch  line  of  the  Pennsyl- 
vania Railroad,  running  north  from  Monmouth  Junction.  The  high 
trap  ridges,  locally  known  as  Tenmile  Mountain  and  Rocky  Hill,  are 
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