180  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
or  three  localities  are  found  beds  of  conglomerates.  These  metamor- 
phic  masses  are  in  all  probability  the  extension  of  the  Huronian  for- 
mation of  Canada. 
Hall  (James),103  in  1862,  describes  the  central  and  northern  areas 
of  Wisconsin  as  consisting  of  the  Azoic  rocks.  These  are  hard  and 
crystalline,  and  in  many  places  are  destitute  of  lines  of  bedding, 
though  they  are  in  reality  as  regularly  stratified  as  the  more  modern 
formations.  Notwithstanding  their  crystalline  character,  the  alterna- 
tion of  beds  of  different  texture  indicates  their  original  different  me- 
chanical 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  were,  and  owe  their  present  character  to 
metamorphism.  These  rocks  are  granitic,  syenitic,  gneissoid,  or 
hornblendic.  In  the  southern  part  of  the  area  of  the  crystalline 
rocks  are  numerous  elevations  of  them  appearing  within  the  limits  of 
the  succeeding  stratified  rocks ;  so  we  know  that  the  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  does  the  Huronian 
system  of  the  Canadian  survey. 
Whittlesey,104  in  1863,  describes  the  copper-bearing  strata  of  Ke- 
weenaw Point  as  extending  southward  across  the  boundary  of  Michi- 
gan 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  mis- 
print it  was  transformed  to  Penokee. 
Passing  from  Lake  Superior  to  south  of  the  iron  range,  the  struc- 
ture 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,  hornblendic;  No.  4,  quartz,  with  slaty  layers,  separated  into 
two  members  by  a  bed  of  magnetic  iron  and  iron  slate;  No.  5,  gran- 
ites and  syenites  of  central  Wisconsin.  This  system  is  everywhere 
stratified  and  conformable  throughout.  On  Bad  and  Montreal  rivers 
are  found  no  masses  of  crystalline  limestone. 
Murrish,  in  1873,  describes  Azoic  rocks  at  Grand  Rapids,  on  the 
Wisconsin  River,  similar  to  those  on  Black  River.  See  summary  in 
Chapter  XII,  section  1,  page  724. 
Irving,105  in  1874,  describes  as  occurring  in  northern  Wisconsin 
four  distinct  groups  of  rocks — the  Laurentian,  Huronian,  Copper- 
bearing,  and  Lower  Silurian.  The  Laurentian  consists  of  granites, 
gneisses,  and  syenites  for  the  most  part,  although  there  may  be  vari- 
ous schist  beds  present.     The  Huronian  rocks  consist  of  siliceous 
