LAKE    SUPERIOR   REGION.  313 
Southward  from  Marquette  are  great  areas  underlain  by  the 
granites,  gneisses,  and  schists  of  the  older  formation,  but  before 
Menominee  River  is  reached  at  least  four  distinct  belts,  occupied  by 
the  newer  iron-bearing  series,  are  crossed.  These  belts  of  newer 
rocks  are  more  closely  folded  than  in  the  Marquette  district,  but 
the  relations  between  the  newer  and  the  older  series  are  identical  with 
those  in  that  district. 
In  the  Penokee  district  of  northern  Wisconsin  and  Michigan  the 
iron-bearing  series  is  highly  tilted  but  unfolded,  and  the  relations  are 
therefore  particularly  plain.  Here  the  lower  of  the  two  unconformi- 
ties is  established  by  (1)  the  fact  that  the  iron-bearing  series  traverses 
lithologically  distinct  areas  of  the  older  or  basement  formation;  (2) 
the  intersection  of  the  older  schistose  rocks  by  granite  which  never 
cut  the  higher  series;  (3)  the  occurrence  in  the  higher  series  of  basal 
conglomerates,  fragments  of  which  are  from  the  underlying  gneiss, 
granite,  and  schist;  and  (4)  the  lithological  contrast  of  the  two  sets  of 
rocks,  the  lower  being  completely  crystalline,  folded,  and  foliated, 
while  the  upper  is  but  little  altered  and  regularly  bedded.  The  upper 
unconformity  is  shown  by  the  manner  in  which  the  flows  of  the 
Keweenaw  series  are  found  in  contact  with  all  members  of  the  iron 
series  at  different  places  along  the  contact  line. 
The  Animikie  series  is  gently  tilted,  and  rests  in  palpable  uncon- 
formity upon  a  folded  series  of  schists,  granites,  and  gneisses.  Above 
it  is  the  Keweenaw  series,  which  bears  the  same  relations  to  the  under- 
lying rocks  as  they  do  to  the  Penokee  series. 
North  of  the  Animikie  beds  are  schistose  iron-bearing  rocks,  which 
extend  from  Vermilion  Lake  to  the  vicinity  of  Knife  and  Saganaga 
lakes.  These  are  flanked  by  gneisses  and  granites,  and  on  account  of 
their  lithological  similarity  to  the  Animikie  rocks  are  taken  to  be  their 
folded  equivalent.  While  there  is  not  here  the  same  palpable  uncon- 
formity as  in  the  other  regions  discussed,  it  is  believed  that  there  are 
two  groups  of  rocks,  the  apparent  conformity  being  due  to  the  intense 
folding. 
There  is,  then,  a  graded  series  in  the  structural  relations  of  the  older 
and  newer  rocks,  from  the  Animikie,  which  lie  upon  the  older  forma- 
tions with  a  slight  inclination,  through  the  Penokee,  which  is  un- 
folded, although  deeply  inclined;  the  typical  Huronian,  which  is 
gently  folded  without  schistose  structure;  the  Marquette,  which  is 
crumpled  between  walls  of  older  schists;  the  Menominee,  in  which 
the  folding  is  so  close  that  the  discordances  are  no  longer  distinct ;  to 
the  rocks  of  Vermilion  Lake,  where  extreme  pressure  has  produced  a 
general  community  of  inclination  between  the  two  groups  of  rocks. 
In  all  these  regions  there  is  a  great  basement  complex  of  crystalline 
