340  PKE-C AMEBIAN    GEOLOGY    OP    NORTH   AMERICA. 
schistosity  and  bedding  stand  nearly  vertical  and  strike  east-north- 
east. This  group  is  intruded  by  granite  masses,  such  as  the  Giants 
Range,  Cacaquabic,  and  Snowbank  granites  and  the  granite  of  White 
Iron  Lake.  The  upper  Huronian  occurs  only  in  the  east  end  of  the 
district,  where  the  westward  continuation  of  the  upper  Huronian  of 
the  Gunflint  district  laps  diagonally  and  unconformably  across  the 
east  end  of  the  Vermilion  district.  The  upper  Huronian  here  is  sim- 
ilar in  all  respects  to  the  metamorphosed  upper  Huronian  of  the  east 
end  of  the  Mesabi  district. 
Rainy  Lake. — In  the  Rainy  Lake  area  is  a  series  dominantly  of  mica- 
ceous schists,  grading  downward  near  its  base  into  green  hornblendic 
and  chloritic  schists,  and  these  in  turn  into  conglomerates.  This 
series  rests  unconformably  upon  the  Keewatin  and  Laurentian  rocks. 
It  is  lithologically  similar  to  the  series  mapped  as  lower  Huronian 
in  the  Vermilion  and  Mesabi  districts  of  Minnesota  and  in  the 
Michipicoten  and  other  districts  of  Ontario.  It  was  originally 
mapped  by  Lawson  under  the  name  "  Coutchiching  "  and  in  small 
part  under  the  name  "  Keewatin."  He  supposed  the  "  Coutchiching  " 
series  to  underlie  the  Keewatin  series,  but  the  reverse  relations  were 
shown  by  Van  Hise  in  1898  and  were  confirmed  by  the  observations  of 
the  international  geological  committee  in  1904.  This  series  is  now 
called  Huronian,  and  the  term  "  Coutchiching  "  has  been  dropped. 
Its  use  has  led  to  much  confusion  because  of  Lawson's  misapprehen- 
sion of  the  stratigraphic  position  of  the  series  to  which  he  applied  the 
term,  and  because  the  term  was  subsequently  used  by  other  geologists 
in  Ontario  and  Minnesota  to  cover  metamorphosed  igneous  and  sedi- 
mentary rocks  of  various  ages,  including  metamorphosed  Keewatin 
rocks.  The  nature  of  certain  of  the  conglomerates  in  the  Huronian 
of  the  southwestern  shore  of  Rainy  Lake  seems  to  indicate  the  possi- 
bility that  both  lower  Huronian  and  middle  Huronian  are  here  rep- 
resented, but  this  is  not  certain. 
Steep  Rock  Lake. — Smyth  describes  the  Steep  Rock  "  series  "  as 
consisting  from  the  base  up  of  conglomerate,  limestone,  ferruginous 
formation,  probably  volcanic  ash,  interbedded  crystalline  traps, 
calcareous  green  schist,  upper  conglomerate,  greenstones  and  green- 
stone schists,  agglomerate,  and  clay  slate.  The  estimated  thickness 
for  the  whole  group  is  4,500  feet.  It  is  believed  that  all  of  these 
rocks  are  older  than  the  Animikie  or  upper  Huronian,  but  whether 
they  comprise  one  or  two  groups  is  not  known.  Possibly  from 
Smyth's  description  both  the  middle  and  lower  Huronian  are  repre- 
sented. The  whole  rests  unconformably  upon  Laurentian  granite 
and  gneisses  and  Keewatin  schists. 
Hunters  Island  and  region  northwest,  north,  and  northeast. — In  the 
Hunters  Island  area  graywackes,  slates,  and  conglomerate,  similar 
in  all  respects  to  the  lower-middle  Huronian  of  the  Vermilion  dis- 
