292  PRE-CAMBRIAN   GEOLOGY   OF   NORTH   AMERICA. 
the  Michipicoten  district.  To  the  lower  part  of  the  Lower  Huronian 
are  referred  the  magnetite  lenses  in  green  schists  of  the  Atikokan 
district  and  the  titaniferous  magnetite  occurring  as  segregations  in 
basic  eruptives,  especially  gabbro.  To  the  Grenville  series,  "  prob- 
ably Huronian,"  are  referred  the  magnetite  and  hematite -ores  asso- 
ciated with  bands  of  crystalline  limestone  and  gneiss  of  eastern  On- 
tario. To  the  Animikie  or  Lower  Huronian  (Upper  Huronian  of 
the  United  States  Geological  Survey)  are  referred  impure  siderite 
and  hematite  occurring  in  the  neighborhood  of  Thunder  Bay  and  also 
near  Algoma.  To  the  Pleistocene  are  referred  the  bog  and  lake  ores 
and  postglacial  magnetic  sands  occurring  widely  in  Ontario,  espe- 
cially in  the  eastern  part. 
Miller,287  in  1903,  gives  a  resume  of  the  occurrences  of  iron  ore  in 
northern  Ontario  and  incidentally  discusses  their  geological  relations. 
Parrs,288  in  1903,  gives  a  brief  preliminary  account  of  the  region 
lying  northeast  of  Lake  Nipigon.  Laurentian,  Huronian,  and  Ani- 
mikie rocks  are  present. 
MgTnnes,289  in  1903,  gives  a  brief  preliminary  account  of  the  geol- 
ogy of  the  region  on  the  northwest  side  of  Lake  Nipigon. 
Miller,290  in  1903,  describes  bowlders  of  nepheline  syenite  near 
Sturgeon  Lake,  northwest  of  Lake  Superior,  indicating  the  occur- 
rence of  rocks  of  this  character  in  the  pre-Cambrian  rocks  farther 
north. 
Smith  and  assistants,291  in  1904,  map  and  describe  the  geology  of 
the  Animikie  or  Loon  Lake  iron-bearing  district  on  the  northwest 
shore  of  Lake  Superior  and  the  country  westward  to  Current  River. 
The  rocks  of  the  district  comprise  Keewatin  green  schists  and  mashed 
porphyries,  Lower  Huronian  graywackes  and  greenstones  intruded  by 
granite,  Upper  Huronian  or  Animikie  iron  formation  and  black  slate 
containing  sills  of  igneous  rocks,  Keweenawan  conglomerates  and 
sandstones  containing  diabase  sills,  and  greenstones  and  porphyrites 
of  unknown  age.  The  Keewatin  and  Lower  Huronian  rocks  form 
the  highlands  back  from  the  Lake  Superior  shore.  The  graywackes 
and  schists  of  these  series  are  much  folded  and  fractured  and  have 
developed  a  nearly  vertical  cleavage-  with  a  general  trend  of  N. 
60°-65°  E.  The  Upper  Huronian  and  Keweenawan  rocks  rest  upon 
the  south  slope  of  this  complex  and  dip  in  general  toward  the  lake 
at  angles  of  5°  to  10°,  with  local  variations  beyond  these  limits. 
Their  distribution  is  complicated  by  two  and  perhaps  more  normal 
faults  striking  about  N.  70°  E.,  probably  intersected  by  another  set 
trending  a  little  east  of  north.  The  downthrow  in  each  case  is  toward 
the  north,  with  the  result  that  the  series  is  repeated  and  occupies  a 
larger  area  than  it  otherwise  would.  Evidence  of  a  pronounced  un- 
conformity between  the  Lower  Huronian  and  the  Keewatin  was  ob- 
served in  a  cut  along  the  Canadian  Pacific  Railway  2  miles  west  of 
