vANiusE.j  LAKE    SUPERIOR    REGION.  147 
crossed  occupied  by  the  newer  iron-bearing  series.  These  belts  of 
newer  rocks  are  more  closely  folded  than  the  Marquette  district,  but 
the  relations  between  the  newer  and  older  series  are  identical  with  that 
district. 
Passing  now  to  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 
unconformities  is  established  (1)  by  the  fact  that  the  iron-bearing  series 
traverses  lithologically  distinct  areas  of  the  older  or  basement  forma- 
tion; (2)  the  intersection  of  the  older  schistose  rocks  by  granite  which 
never  cut  the  higher  series;  (8)  the  occurrence  in  the  higher  series  of 
basal  conglomerates,  fragments  of  which  are  from  the  underlying  gneiss, 
granite,  and  schist;  (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  uncon- 
formity 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  dif- 
ferent places  along  the  contact  line. 
The  Animikie  series  is  gently  tilted,  and  rests  in  palpable  unconform- 
ity upon  a  folded  series  of  schists,  granites,  and  gneisses.  Above  it  is 
the  Keweenaw  series,  which  bears  the  same  relations  to  the  underlying 
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- 
formities 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  unfolded, 
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  district,  where  the  folding  is  so 
close  that  the  discordances  are  no  longer  distinct;  to  the  Vermilion 
lake  district,  where  extreme  pressure  has  produced  a  general  commu- 
nity of  inclination  between  the  two  groups  of  rocks.  There  is  then 
in  all  these  regions  a  great  basement  complex  of  crystalline  schists, 
gneisses,  and  granites,  above  which,  separated  by  a  great  structural 
hiatus,  is  the  Huronian  group,  mainly  of  detrital  rocks,  which  is  fol- 
lowed in  turn,  after  a  severe  structural  break,  by  the  Keweenaw  group, 
upon  the  eroded  edges  of  which  rest  the  Potsdam  or  Upper  Cambrian 
sandstone.  For  the  combination  of  clastic  series  above  the  basement 
complex  and  below  the  Potsdam  sandstone  the  system  name  Agnoto- 
zoic  is  proposed. 
