HIGHLANDS    OF    NEW    JERSEY.  641 
Wolff,113  in  1895,  reaches  the  following  conclusions  as  a  result  of 
his  detailed  study  of  the  Highlands  of  New  Jersey  in  the  vicinity  of 
Hibernia.  The  rocks  are  found  to  consist  of  distinct  bands  of  gneiss 
which  can  be  recognized.  These  layers  have  once  been  nearly  hori- 
zontal, and  are  folded  into  an  anticlinal  dome  which  has  the  charac- 
teristics of  ordinary  folds  and  a  distinctly  recognizable  pitch.  The 
rocks  of  the  series  have  a  top  and  a  bottom,  the  bottom  rocks  being  at 
the  center  of  the  dome  and  the  top  rocks  at  the  periphery.  One  char- 
acteristic horizon,  a  garnet-biotite-graphite  gneiss,  must  once  have  ex- 
isted over  a  large  part  of  the  present  area,  and  the  same  is  probably 
true  of  the  lower  horizons.  The  foliation,  in  part  at  least,  is  parallel 
to  the  bounding  planes  of  the  different  layers  of  rocks.  The  crystal- 
lization of  the  rock  occurred  during  <>r  after  the  action  of  the  com- 
pressing force  which  folded  the  rocks  and  produced  pitch,  but  not 
before,  since  this  structure  is  inherent  in  the  shape  of  the  minerals  as 
they  crystallized.  These  facts  favor  the  view  that  the  series  is  a  sedi- 
mentary one,  in  which  metamorphism  and'recrystallization  took  place 
contemporaneously  with  the  folding  and  without  fusion,  and  there- 
fore that  it  is  of  Algonkian  age. 
Westgate,114  in  189G,  describes  and  maps  the  geology  of  the  north- 
ern part  of  Jenny  Jump  Mountain,  in  Warren  County,  X.  J.  The 
main  ridge  of  the  mountain  is  formed  chiefly  of  gneisses,  comprising 
many  varieties.  These  are,  from  northwest  to  southeast,  and  also,  ac- 
cording to  the  banding,  from  base  to  top,  (1)  granitoid  biotite-horn- 
blende  gneiss,  containing  narrow  bands  of  biotite-hornblende  gneiss ; 
(c2)  hornblende-pyroxene  gneiss ;  (3)  biotite  gneiss;  (1)  dark  biotite- 
hornblende  gneiss;  (5)  granitoid  biotite-hornblende  gneiss;  and  (6) 
dark  biotite-hornblende  gneiss  and  gray  micaceous  gneiss.  Certain 
of  the  dark  hornblende  gneisses  have  been  so  extensively  altered  as 
to  be  called  epidote  rocks.  The  gneisses  are  in  general  granitoid  and 
massive,  and  there  is  a  conspicuous  absence  of  schistose  rocks  and 
crumpling  of  the  banding,  the  banding  over  wide  areas  having  uni- 
form strike  and  dip. 
Along  the  southeast  side  of  the  mountain,  at  the  northeast  end  of 
the  mountain,  and  in  two  isolated  outcrops  within  the  gneisses  of  the 
main  ridge  are  areas  of  white  crystalline  limestone.  The  limestone  is 
in  all  cases  closely  associated,  and  perhaps  interbanded,  with  the  dark 
biotite-hornblende  gneiss  and  gray  micaceous  gneiss  (Nos.  1  and  6 
above),  and  at  the  northeast  end  of  the  mountain  also  with  quartz 
pyroxene  rock. 
Cutting  both  gneisses  and  limestone  are  pegmatite,  diabase,  and 
amphibolite  or  granular  diorite. 
The  origin  and  age  of  the  gneisses  are  doubtful.  The  presence  of 
limestone  belts  closely  associated  and  perhaps  interbanded  with  the 
55721— Bull.  3G0— 09 41 
