LAKE    SUPERIOR   REGION.  199 
formed  as  a  result  of  combined  igneous  action  and  the  folding  of 
sedimentary  strata  and  erosion. 
Winchell  (N.  H.),145  in  1881,  gives  many  details  as  to  the  rocks  of 
northeastern  Minnesota.  At  Pigeon  Point  is  a  massive  bedded  or 
jointed  formation  like  that  at  Duluth,  with  which  it  may  be  paral- 
lelized. The  latter  belongs  to  the  Cupriferous  series  and  the  former 
to  the  Animikie,  so  that  the  Animikie  appears  to  be  a  downward  ex- 
tension of  the  Cupriferous.  At  Mountain  Lake  the  hills  are  short 
monoclines  of  gray  quartzite,  with  beds  of  argillaceous  and  black 
slate,  dipping  to  the  southward  usually  at  an  angle  of  8°  or  10°,  and 
covered  with  a  greater  or  less  thickness  of  trap  rocks.  In  beds  gener- 
ally less  than  50  feet,  but  sometimes  150  feet  thick,  the  trap  and  slate 
dip  together,  so  that  the  hills  have  gradual  slopes  toward  the  south, 
and  steep  or  perpendicular  slopes  toward  the  north.  The  quartzite 
must  be  an  immense  formation,  as  it  is  seen  at  Grand  Portage  and  all 
over  Pigeon  Point,  and  on  the  islands  of  the  point.  The  quartzite 
formation  of  Gunflint  Lake  seems  to  graduate  downward  into  the 
irony  and  carbonaceous  Gunflint  beds.  A  greenish,  schistose,  por- 
phyritic  rock,  cut  by  veins  of  milk  quartz,  is  found  in  a  nearly  ver- 
tical attitude  on  Gunflint  Lake.  This  is  supposed  to  be  the  Canadian 
Huronian,  and  underlies  the  quartzite  and  Gunflint  beds  apparently 
unconf ormably ;  at  least,  it  is  a  distinct  formation  from  the  Grand 
Portage  slates.  The  quartzite  is  locally  a  quartzite  conglomerate. 
The  Knife  Lake  serpentinous  quartzite  is  regarded  as  Huronian.  On 
the  south  side  of  Vermilion  Lake  are  beds  of  jasper  and  iron  which 
are  regarded  as  the  equivalent  of  the  Gunflint  beds.  These  are  con- 
formable with  the  magnesian  schists  and  slates,  which  are  in  a  ver- 
tical attitude.  They  pass  down  into  the  schists,  and  in  places  the 
schists  and  schistose  structure  penetrate  the  jasper  and  iron.  It  is 
suggested  that  the  apparent  conformity  between  the  ferruginous  beds 
and  the  underlying  slates  and  schists  is  only  a  superinduced  one,  the 
original  bedding,  which  may  have  been  nearly  horizontal,  having  been 
obliterated  by  the  change. 
Winchell  (N.  H.),14,i  in  1881,  describes  the  Cupriferous  series  of 
Minnesota  as  having  a  wide  extent.  In  passing  from  the  shore  of 
Lake  Superior  it  gradually  becomes  more  changed  and  crystalline. 
The  tilted  red  shales,  conglomerates,  and  sandstones  at  Fond  du 
Lac  are  the  same  as  those  associated  with  the  igneous  rocks  all  along 
the  shore.  At  Fond  du  Lac  they  lie  on  white  quartz  pebbly  conglom- 
erate a  few  feet  in  thickness,  which  rests  unconformably  on  the  roof- 
ing slates  of  the  Huronian,  the  same  formation  that  succeeds  to  the 
red  rock  formation  at  Ogishki  Manissi  and  Knife  lakes,  northwesl 
of  Grand  Marais.  The  Cupriferous  series  differs  from  the  Upper 
Laurentian  or  Norian  only  in  the  absence  of  beds  of  limestone,  but, 
