68  PRE-CAM BRIAN    ROCKS    OF    NORTH    AMERICA.  [bull. 86. 
Lawson,38  in  1890,  discusses  the  internal  relations  and  taxonomy  of 
the  Archean  of  central  Canada.  The  Keewatin  and  Coutchiching  are 
again  described  and  the  characteristic  contacts  which  they  have  with 
the  Laurentian.  To  the  upper  division,  the  Keewatin  and  Coutchiching, 
since  they  are  sedimentary  rocks,  the  principles  of  stratigraphical  geol- 
ogy apply,  and  to  cover  these  two  series  is  proposed  the  term  Ontarian, 
of  systemic  value.  The  principles  applicable  to  the  lower  division,  the 
Laurentian,  are  those  of  eruptive  geology,  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  suberustal  magma. 
Bell,39  in  1800,  gives  the  following  as  the  chief  Huronian  areas 
about  lake  Superior,  in  Ontario.  An  important  area  lies  around  Michi- 
picoten  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  the 
Pic  river  eastward  or  inland  to  Nottamasa garni  lake,  and  westward 
mingled  with  granites  and  greenstones,  to  Nipigon  bay.  Two  exten- 
sive belts  run  eastward  from  lake  Mpigon,  one  of  which  crosses  Long- 
lake.  West  of  Thunder  bay,  and  stretching  to  the  international 
boundary  line,  there  is  a  large  area  which  gives  off  arms  to  the  north- 
east and  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, 
which  has  been  already  alluded  to,  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  Sturgeon  lakes  lie  within  this  belt. 
The  Huronian  is  divided  into  a  lower  and  upper  division,  although 
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  are  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  enu- 
merated 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,  gran- 
ites and  syenites,  impure,  banded,  and  schistose  iron  ores,  dolomites  and 
imperfect  gneisses.  Among  the  commoner  of  the  rocks  of  this  division 
are  tine  grained  mica-schists  and  dark  green  dioritic  or  hornblendic 
schists.     Two  kinds  of  conglomerates  are  also  abundant,  one  having  an 
