284  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
that  the  Huronian,  as  recognized  in  these  regions,  is  really  younger 
and  overlies  the  upturned  edges  of  the  rocks  described  as  Huronian  in 
the  northern  Archean. 
Van  Hise,272  in  1898,  visited  the  Rainy  Lake  and  Lake  of  the 
Woods  districts.  Observations  made  in  the  Shoal  Lake  area,  along 
the  south  side  of  Rainy  Lake,  led  to  the  conclusion  that  the  Coutchi- 
ching  is  for  the  most  part  stratigraphically  higher  than  the  rocks 
mapped  as  Keewatin;  in  other  words,  that  Lawson's  succession 
should  be  reversed.  The  schists  of  the  northern  part  of  the  lake, 
mapped  as  Keewatin,  were  found  to  be  intruded  by  granites  with 
normal  intrusive  contacts.  No  evidences  of  subcrustal  fusion  were 
observed. 
McInnes,273  in  1899,  describes  the  geology  of  the  Seine  River  and 
Lake  Shebandowan  map  sheets,  which  cover  an  area  extending  west 
and  northwest  of  Port  Arthur,  Ontario.  Laurentian  granites  and 
gneisses  with  many  variations  occupy  three- fourths  of  the  area.  The 
relations  to  the  overlying  Keewatin  and  Coutchiching  rocks,  wher- 
ever they  have  been  found  in  contact,  have  been  those  of  intrusion. 
The  Huronian  is  represented  by  Coutchiching  and  Keewatin  rocks. 
Coutchiching  mica  schists  and  fine-grained  gneisses,  a  continuation 
of  Lawson's  Coutchiching  in  the  Eainy  River  district  to  the  west, 
enter  the  area  of  the  Seine  River  sheet  on  the  west  side.  However, 
toward  the  east  these  rocks  become  associated  with  large  quantities 
of  gneisses,  and  for  the  eastern  two- thirds  of  the  Seine  River  area 
and  for  the  entire  Lake  Shebandowan  area  the  gneisses  are  predomi- 
nant and  the  belt  is  mapped  as  Laurentian.  In  other  parts  of  the 
district  the  Keewatin  schists,  near  their  contact  with  the  Laurentian 
gneisses,  assume  a  character  exactly  similar  to  the  Coutchiching 
schists  and  associated  gneisses,  and  could  not  be  lithologically  dis- 
tinguished. Indeed,  the  Coutchiching  seems  to  be  an  extremely 
altered  phase  of  the  Keewatin. 
In  long  bands  infolded  with  the  Laurentian  and  conforming  in 
strike  with  the  foliation  of  the  gneiss  are  Keewatin  rocks  varying 
greatly  in  width.  They  vary  in  composition  from  extremely  basic 
igneous  masses  and  their  derived  products  to  acidic  quartz  porphy- 
ries and  their  derived  products,  and  include  also  quartzites,  con- 
glomerates, and  slates.  The  basic  rocks  form  the  largest  volume 
of  the  rocks  of  the  series.  The  series  is  separated  lithologically  in 
mapping  into  three  divisions.  There  can  be  no  doubt  that  the  Kee- 
watin here  includes  rocks  which  are  of  widely  differing  age. 
Overlying  unconformably  the  Keewatin  rocks  is  the  Steep  Rock 
Lake  series,  so  named  from  its  occurrence  in  the  neighborhood  of  this 
lake.  The  series  is  mapped  as  an  upper  division  of  the  Keewatin 
series.  As  described  by  Smyth  it  comprises  conglomerate,  limestone, 
clay  slate,  and  various  basic  volcanic  and  intrusive  rocks.     Because 
