LAKE    SUPERIOR   REGION.  291 
The  Upper  Huronian  rocks  are  represented  principally  by  the 
Dore  conglomerate,  occurring  typically  at  the  mouth  of  Dore  River 
and  thence  eastward  beyond  Michipicoten  Harbor,  and  to  a  less  ex- 
tent in  other  parts  of  the  district.  This  conglomerate  is  unconform- 
ably  above  the  Lower  Huronian  rocks  of  the  district.  It  contains 
pebbles  of  granite,  felsite,  conglomerate,  granular  silica  of  the  iron 
formation,  and  breccia. 
The  Dore  conglomerate  is  cut  by  acidic  intrusives  in  dikes  and 
bosses.    These  are  the  latest  rocks  of  the  region. 
The  Laurentian  granites  and  gneisses  have  not  been  studied  in  de- 
tail in  the  Michipicoten  district,  but  their  associations  with  both 
Lower  and  Upper  Huronian  prove  them  to  be  post-Huronian  erup- 
tive masses. 
Coleman,281  in  1902,  discusses  the  origin  of  the  rock  basins  of  Boyer 
and  Sayers  lakes  of  the  Michipicoten  district  of  Canada,  the  former 
containing  the  Helen  iron-ore  body.  He  holds  the  lake  basins  to  have 
resulted  from  the  solution  of  the  iron-bearing  rocks  long  before  glacial 
time. 
Coleman,28-  in  1902,  describes  nepheline  and  other  syenites  near 
Port  Coldwell,  Ontario,  and  calls  attention  to  their  widespread  distri- 
bution in  Ontario  and  the  United  States. 
McInnes,283  in  1902,  gives  a  brief  preliminary  account  of  the  nature 
and  distribution  of  the  Laurentian  and  Huronian  rocks  in  the  region 
southeast  of  Lac  Seul. 
Wilson,284  in  1902,  gives  a  brief  preliminary  account  of  the  nature 
and  distribution  of  the  Laurentian,  Huronian,  and  Cambrian  rocks 
in  the  region  west  of  Nipigon  Lake  and  River.  The  Huronian  is  rep- 
resented by  a  highly  ferruginous  quartzite  occurring  in  a  small  area 
commencing  near  the  southeast  corner  of  Black  Sturgeon  Lake  and 
extending  southeast  to  the  vicinity  of  Nonwatinose  Lake.  Animikie 
sediments  and  traps  assigned  to  the  Cambrian  make  up  a  large  part 
of  the  area.     Dolomite  is  conspicuous  in  this  series. 
Parks,28*  in  1902,  gives  a  brief  preliminary  account  of  the  area 
east  of  Nipigon  Lake  and  River. 
Coleman,280  in  1902,  gives  results  of  an  examination  of  the  iron 
ranges  of  northwestern  Ontario,  principally  the  Mattawan,  Atikokan, 
Sleep  Rock  Lake,  and  other  districts  along  the  Canadian  Northern 
Railway,  the  Slate  Islands  in  Lake  Superior,  and  near  Dryden,  on 
(lie  Canadian  Pacific.  The  description  of  the  details  of  the  districts 
contains  but  few  references  to  general  stratigraphy  and  correlation, 
but  at  the  end  a  general  classification  of  the  iron  ores  of  Canada  is 
given.  To  the  upper  part  of  the  Lower  Huronian  (Animikie  of  the 
United  States  Geological  Survey)  are  referred  the  siliceous  and 
sideritic  iron  ranges  occurring  in  practically  every  iron-bearing  area 
in  Ontario,  but  being  mined  at  only  one  place — the  Helen  mine,  in 
