334  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
against  the  greenstone  without  intervening  fragmental  material. 
Mining  operations  and  the  surface  distribution  of  the  iron-bearing 
formation,  particularly  the  occurrence  of  the  main  belts  in  synclinal 
areas  adjacent  to  lower  Huronian  sediments,  indicate  that  this  for- 
mation, in  many  places  at  least,  rests  on  top  of  the  greenstone  and 
has  been  infolded  with  it;  but  there  is  little  opportunity  to  determine 
the  relations  of  many  of  the  iron-formation  bands,  and  it  has  been 
thought  probable  that  some  may  be  interbedded  with  greenstone 
flows.  Indeed,  interbedding  seems  almost  certainly  to  explain  the 
relations  of  the  greenstone,  iron  formation,  and  Huronian  sediments 
at  the  east  end  of  the  Ely  iron-bearing  trough.  In  this  connection 
it  is  interesting  to  note  that  at  Schreiber  Bay,  on  the  north  shore  of 
Lake  Superior,  a  well-bedded  iron-bearing  formation  of  the  Animikie 
group  rests  on  granite  without  intervening  fragmental  material, 
although  a  short  distance  away  separating  clastic  material  is  found. 
As  elsewhere,  the  Laurentian  series  of  the  Archean  in  the  Ver- 
milion district  is  intrusive  into  the  greenstones  and  iron  formation 
of  the  Keewatin.  It  consists  of  granite  porphyries  and  granites,  the 
latter  chiefly  almost  massive,  but  showing  subordinate  amounts  of 
schistose  granite.  The  granites  occur  for  the  most  part  in  the  great 
area  lying  north  and  east  of  the  Vermilion  range.  Immediately 
adjacent  to  the  range  they  are  known  as  the  "  Vermilion  Lake/' 
"  Trout,"  "  Burntside,"  "  Basswood,"  and  "  Saganaga  Lake  "  granites. 
Along  the  contact  of  the  Keewatin  there  are  considerable  belts  of 
hornblendic  schist  and  gneiss,  which  are  the  Keewatin,  metamor- 
phosed by  and  intermingled  with  the  granite.  The  granites  of  Ver- 
milion Lake  presumably  extend  northward  into  Canada  and  connect 
with  granites  mapped  by  the  Canadian  geologists,  but  again  informa- 
tion is  not  available  which  will  allow  the  drawing  of  boundaries 
between  granite  belonging  to  the  basement  complex  and  granites  of 
later  age,  considerable  masses  of  which  appear  in  the  Canadian 
districts  to  the  north. 
Lake  of  the  Woods  and  Rainy  Lake. — In  the  districts  of  Lake  of 
the  Woods  and  Kainy  Lake  the  Keewatin  series  of  the  Archean  is 
well  represented,  occupying  a  large  part  of  the  area  mapped  in  detail. 
Indeed,  the  name  KeewTatin  was  first  applied  to  the  rocks  of  this 
series  by  Lawson  in  the  Lake  of  the  Woods  area.  The  Keewatin 
consists  of  massive  and  schistose  greenstones  with  ellipsoidal  and 
surface  phases,  perhaps  in  part  water  deposited,  and  contains  small 
amounts  of  normal,  black,  sedimentary,  and  apparently  interbedded 
slate.  Iron-bearing  formation  similar  to  that  in  the  Vermilion  dis- 
trict is  apparently  lacking,  but  in  its  place  are  narrow  layers  and 
lenses  of  cherty  and  ferruginous  dolomite,  less  than  3  feet  wide, 
which  have  almost  identically  the  same  relations  with  the  greenstones 
and  green  schists  as  has  the  iron-bearing  formation  in  the  Vermilion 
district.    The  series  is  intruded  and  highly  metamorphosed  by  Lau- 
