LAKE    SUPERIOR   REGION.  237 
rocks  of  the  Lower  Keewatin  doubtless  also  underlie  most  of  the  cen- 
tral and  southwestern  part  of  the  State  as  far  as  the  Minnesota  River. 
Here  they  dip  beneath  the  later  formations  in  the  southwestern  por- 
tion of  the  State,  and  probably  occupy  a  wide  patch  in  South  Dakota. 
South  of  the  Giants  range  they  occur  also,  but  as  they  are  covered  by 
the  gabbro  and  Animikie  toward  the  east  and  the  drift  deposits  of  the 
St.  Louis  Valley  toward  the  west  their  geographic  boundaries  arc 
mostly  unknown.  They  appear  in  the  central  and  western  portions  of 
Carlton  County,  where  their  line  of  separation  from  the  Upper  Kee- 
watin is  obscure,  and  in  the  central  and  western  portions  of  Morrison 
County.  The  Lower  Keewatin  marble  is  seen  at  Lake  Ogishke-Mun- 
cie  and  at  Pike  Rapids  on  the  Mississippi. 
The  Lower  Keewatin  was  terminated  by  a  period  of  extensive  fold- 
ing and  intrusions  of  granite  and  basic  rocks. 
The  Pewabic  quartzite  belongs  with  the  Keewatin,  but  whether  to 
the  Lower  or  Upper  Keewatin  is  not  known.  This  formation  includes 
altered  quartzites  and  iron  ores  between  the  granite  and  gabbro  in  the 
immediate  vicinity  of  Birch  Lake,  and  small  patches  of  similar  rocks 
in  sec.  30,  T.  62  N.,  R.  10  W. ;  on  the  south  shore  of  Disappointment 
Lake;  on  the  north  shore  of  Fraser  Lake;  on  the  south  shore  of  Gab- 
beinichigamma ;  at  Akley  Lake,  forming  the  so-called  Akley  Lake 
series  extending  from  the  west  side  of  sec.  34,  T.  65  N.,  R.  5  W.,  to  the 
eastern  part  of  sec.  27,  T.  65  N.,  R.  4  W. 
The  Upper  Keewatin  occurs  in  troughs  in  the  Lower  Keewatin, 
and  particularly  in  one  main  trough  the  axis  of  which  is  traceable 
from  Vermilion  Lake  to  Saganaga  Lake.  The  northern  arm  of  this 
syncline,  consisting  of  granites,  gneisses,  associated  mica  schists,  and 
in  some  places  earlier  greenstones,  extends  from  the  northern  part  of 
Vermilion  Lake  through  Basswood  Lake  to  the  northern  side  of 
Hunters  Island.  The  southern  arm,  consisting  of  Lower  Keewatin 
.  green  schists  and  other  schists,  penetrated  by  the  granite  of  the  Giants 
range,  extends  from  Pokegama  Falls  on  the  southwest  toward  the 
northeast,  until  cut  out  by  the  encroachment  of  the  gabbro  from  the 
south.  The  Upper  Keewatin  consists  very  largely  of  conglomerates, 
but  also  includes  graywackes,  argillites,  quartzites,  and  jaspilites,  in 
general  coarser  than  those  of  the  Lower  Keewatin.  Volcanic  rocks 
are  less  important  than  in  the  Lower  Keewatin,  although  still  present. 
There  is  no  general  order  of  succession  in  the  Upper  Keewatin,  except 
that  it  is  in  general  conglomeratic  at  the  bottom. 
After  Upper  Keewatin  time  both  the  Lower  and  the  Upper  Kee- 
watin were  subjected  to  another  folding,  the  axis  of  which  had  a 
general  parallelism  with  the  earlier  folding,  with  the  result  that  the 
Upper  Keewatin  lies  in  narrow  synclines  in  the  Lower  Keewatin  and 
in  places  is  nearly  or  quite  vertical. 
