LAKE    SUPERIOR   REGION.  2 
ogy,  since  these  rocks  are  of  igneous  origin.  In  the  Laurentian  there 
are  at  least  two  generations  of  rocks  which  are  distinguishable  in  the 
Hunter  Island  district,  but  both  are  the  result  of  the  crystallization 
of  a  subcrustal  magma. 
Bell,254  in  1890,  gives  the  following  as  the  chief  Huronian  areas 
about  Lake  Superior,  in  Ontario.  An  important  area  lies  around 
Michipicoten,  at  the  northeast  angle  of  Lake  Superior,  running  for  60 
miles  west  and  20  miles  south  of  that  point,  and  extending  inland  to 
Dog  Lake,  a  distance  of  45  miles.  Another  large  area  stretches  from 
Pic  River  eastward  or  inland  to  Nottamasagami.  Lake,  and  westward, 
mingled  with  granites  and  greenstones,  to  Nipigon  Bay.  Two  exten- 
sive belts  run  eastward  from  Lake  Nipigon,  one  of  which  crosses  Long 
Lake.  West  of  Thunder  Bay,  and  stretching  to  the  international 
boundary  line,  is  a  large  area  which  gives  off  arms  to  the  northeast 
and  the  southwest;  and  several  belts  and  compact  and  straggling 
areas  occur  between  this  and  the  Lake  of  the  Woods  basin,  one  of 
which  follows  the  course  of  the  Seine  River.  The  Lake  of  the  Woods 
area  occupies  the  whole  breadth  of  the  northern  division  of  that  lake. 
An  important  belt  starts  between  Rainy  Lake  and  Lake  of  the  Woods, 
and  running  northeastward  has  a  breadth  of  45  miles  where  it  crosses 
the  line  of  the  Canadian  Pacific  Railway.  Minnietakie  and  Stur- 
geon lakes  lie  within  this  belt. 
The  Huronian  is  divided  into  a  lower  and  an  upper  division,  al- 
though no  horizon  has  been  agreed  upon  at  which  to  draw  the  line 
between  the  two  even  locally.  There  is  no  evidence  whatever  that 
the  two  divisions  are  unconformable  or  that  the  lower  part  of  the 
upper  division  consists  of  basal  conglomerates.  Conglomerates  are 
found  indifferently  throughout  both  lower  and  upper  divisions. 
The  lower  division  includes  the  Keewatin  of  Lawson  and  its  equiva- 
lents. It  consists  largely  of  a  variety  of  crystalline  schists,  in  which 
the  prevailing  color  is  dark  green  or  gray.  Among  these  may  be 
enumerated  micaceous,  dioritic,  chloritic,  argillaceous,  hornblendic, 
talcoid,  felsitic,  epidotic,  siliceous,  dolomitic,  and  plumbagenous. 
There  are  also  crystalline  diorites  or  diabases  of  various  shades  of 
gray  and  greenish  gray  (mostly  dark),  argillaceous  and  dioritic  slate 
conglomerates,  granites  and  syenites,  impure,  banded,  and  schistose 
iron  ores,  dolomites,  and  imperfect  gneisses.  Among  the  commoner 
of  the  rocks  of  this  division  are  fine-grained  mica  schists  and  dark- 
green  dioritic  or  hornblendic  schists.  Two  kinds  of  conglomerates 
arc  also  abundant,  one  Inning  an  argillaceous  matrix  with  rounded 
pebbles  of  syenite  and  granite  of  various  kinds,  and  some  of  the  other 
Huronian  rocks,  but  very  seldom  of  gneiss;  the  other  with  a  dioritic 
matrix,  and  often  with  rounded  pebbles  also.  But,  in  perhaps  the 
majority  of  cases,  what  were  formerly  considered  as  pebbles  are  con- 
cretions of  a  lenticular  form,  and  differ  but  slightly  from  the  matrix 
