106  PRE-CAMBRIAN   ROCKS    OF   NORTH   AMERICA.  [bull.  86. 
Lapham,120  in  1860,  describes  the  Penokee  iron  range.  Here  is  found 
a  mountain  mass  of  iron  ore  in  an  ancient  chloritic  slate,  which  rests 
upon  a  light  colored  quartz  rock.  Above  and  north  of  the  ore  the  slate 
is  hardened,  probably  by  some  volcanic  agency.  The  whole  series  dip 
to  the  north. 
Hall  (James),121  in  1861,  describes  the  quartzite  ranges  of  northern 
Wisconsin,  and  particularly  those  of  Spirit  lake,  as  having  been  original 
stratified  sandstones  which  have  undergone  subsequent  metamorphism. 
These  rocks  are  folded  with  their  axes  lying  in  an  east  and  west  direc- 
tion and  had  become  uplifted  and  metamorphosed  before  the  commence- 
ment of  the  Potsdam  era.  In  the  quartzites  in  two  or  three  localities 
are  found  beds  of  conglomerates.  These  metamorphic  masses  are  in  all 
probability  the  extension  of  the  Huronian  formation  of  Canada. 
Hall  (James),122  in  1862,  describes  the  central  and  northern  areas  of 
Wisconsin  as  consisting  of  the  Azoic  rocks.  These  are  hard  and  crystal- 
line, are  often  destitute  of  lines  of  bedding,  though  they  are  in  reality 
as  regularly  stratified  as  the  more  modern  formations.  Notwithstand- 
ing their  crystalline  character,  their  alternation  of  beds  of  different 
texture  indicates  their  original  different  mechanical  conditions  as  clearly 
as  in  any  of  the  unaltered  strata.  They  were  deposited  precisely  as 
clay,  sand,  and  limestone  strata  of  more  recent  geological  periods,  and 
owe  their  present  character  to  metamorphism.  These  rocks  are  gran- 
itic, syenitic,  gneissoid,  or  hornblendic.  In  the  southern  part  of  the 
area  of  the  crystalline  rocks  are  numerous  elevations  of  them  appear- 
ing within  the  limits  of  the  succeeding  stratified  rocks,  so  that  we  know 
that  these  latter  are  of  later  date.  North  of  the  Azoic  rocks  is  the 
range  of  trap,  conglomerate  and  sandstone  bordering  Lake  Superior 
and  known  as  the  copper  region.  The  quartzite  ranges  of  Baraboo  and 
Necedah  hold  the  same  position  relative  to  the  Potsdam  sandstone  as 
the  Huronian  system  of  the  Canadian  survey. 
Whittlesey,123  in  1863,  describes  the  copper-bearing  strata  of  Ke- 
weenaw point  as  extending  southward  across  the  boundary  of  the 
state  of  Michigan  into  Wisconsin,  a  distance  of  160  miles.  The  order 
of  rocks  along  the  line  is  everywhere  the  same.  Beyond  the  copper 
range,  which  is  nearer  to  lake  Superior,  is  a  second  range  known  as 
the  iron  range,  and  to  this  the  name  Pewabik  was  applied,  although  by 
a  misprint  it  was  transformed  to  Penokee. 
Passing  from  lake  Superior  to  south  of  the  iron  range,  the  structure  in 
descending  order  is  as  follows:  Formation  No.  1,  Potsdam  sandstone, 
consisting  of  sandstones,  conglomerates,  black  slates,  and  alternations 
of  trap  and  sandstone;  No.  2,  Trappose,  in  two  members;  No.  3,  Horn- 
blendic; No.  4,  Quartz,  with  slaty  layers,  separated  into  two  members 
by  a  bed  of  magnetic  iron  and  iron  slate;  No.  5,  Granites  and  syenites 
of  central  Wisconsin.  This  system  is  everywhere  stratified  and  con- 
formable throughout.  On  the  Bad  and  Montreal  rivers  are  found  no 
masses  of  crystalline  limestone. 
