286  PKE-CAMBRIAN   GEOLOGY   OF   NORTH   AMERICA. 
erate,  made  up  chiefly  of  underlying  Laurentian  rocks,  is  common  on 
the  north  shore,  which  apparently  has  not  been  found  on  the  south 
shore. 
Coleman,275  in  1900,  gives  a  general  account  of  a  visit  to  all  the 
iron  and  copper  regions  of  the  Lake  Superior  country.  For  the 
ranges  on  the  United  States  side  of  the  boundary  no  facts  are  given 
not  found  in  the  published  reports.  On  the  Canadian  side  of  the 
boundary  the  Michipicoten  range,  the  iron  formation  near  Dog 
River,  and  the  siliceous  iron  ores  of  Batchawana  Bay  are  described. 
In  the  Michipicoten  range  the  Helen  mine  in  particular  is  referred 
to.  In  general,  the  rocks,  including  the  ore  at  this  mine,  have  all 
the  appearance  of  Lower  Huronian  or  Keewatin  rocks,  as  in  the 
Vermilion  district,  and  not  those  of  the  Upper  Huronian  or  Ani- 
mikie,  as  in  the  Mesaba. 
Near  Dog  River  are  iron-formation  rocks  similar  to  those  extend- 
ing northeast  from  Michipicoten  Bay.  It  is  thought  probable  that 
the  two  may  connect. 
The  occurrence  and  relations  of  iron-formation  material  northeast 
from  Michipicoten  Bay  and  near  Dog  River  are  indicated  on  a  sketch 
map.  * 
Coleman,270  in  1900,  as  a  result  of  an  examination  of  the  new 
Michipicoten  iron  district  and  the  consideration  of  other  iron-forma- 
tion areas  in  Ontario,  has  collected  facts  which  seem  to  throw  some 
light  on  the  relative  ages  of  the  different  areas  mapped  as  Huronian 
on  the  north  shore.  In  the  Michipicoten  district  iron-formation 
material,  consisting  of  banded  ferruginous  sandstones,  cherts,  and 
jaspers,  standing  nearly  vertical,  extends  from  Little  Gros  Cap  north- 
eastward for  20  miles;  then  bending  to  the  north  and  west,  it  takes 
a  westerly  direction  for  more  than  30  miles.  The  width  of  the  belt 
is  but  a  few  hundred  yards. 
Sandstones  of  the  same  peculiar  type  occur  at  Little  Turtle  Lake, 
east  of  Rainy  Lake,  and  near  Fort  Frances,  on  Rainy  River,  as  well 
as  at  the  Scramble  gold  mine,  near  Rat  Portage,  on  Lake  of  the 
Woods.  Thin  sections  of  these  rocks  show  the  same  polygonal  shapes 
of  the  grains  of  quartz,  and  more  or  less  iron  ore  is  associated  with 
specimens  from  each  locality.  It  is  very  probable,  then,  that  the 
same  horizon  exists  at  points  far  to  the  west  of  Lake  Superior. 
Turning  toward  the  east,  specimens  very  like  the  jaspery  varieties 
of  the  Michipicoten  iron  range  are  found  interbedded  with  iron  ores 
near  Lakes  Wahnapitae  and  Temagami,  between  Sudbury  and  Ottawa 
River. 
At  Batchawana  Bay,  at  the  southeast  end  of  Lake  Superior,  a 
siliceous  rock  with  narrow  bands  of  magnetite  occurs,  which  is  prob- 
ably the  equivalent  of  the  Michipicoten  rock. 
