GEEAT   NORTHERN    INTERIOR   OF   CANADA.  537 
including  gneisses  and  granites  classed  as  Laurentian,  and  folded 
schists  and  greenstones  classed  as  Huronian. 
The  Laurentian  rocks  prevail  over  a  much  greater  area  than  the 
Huronian  rocks,  being  seen  along  White  and  Berens  rivers,  on  Lac 
Seul,  and  on  English  and  Matawan  rivers.  They  are  gneisses  and 
granites,  the  latter  in  places  apparently  intrusive  in  the  former, 
as  along  the  headwaters  of  Berens  River.  The  granites  are  occasion- 
ally intrusive  also  in  the  Huronian  to  the  south. 
The  Huronian  rocks  are  a  series  of  schists,  limestones,  and  water- 
deposited  volcanic  materials.  They  occur  in  two  main  areas.  The 
eastern  one  is  in  the  vicinity  of  Clearwater  and  Woman  lakes.  The 
eastern  boundary  of  this  area  has  not  been  defined;  to  the  west  the 
Huronian  is  in  contact  with  the  Laurentian.  From  the  southwestern 
part  of  the  area  a  belt  extends  southwest  to  the  vicinity  of  Shallow 
Lake.  The  western  area  of  Huronian  occurs  in  the  vicinity  of  Red 
Lake,  and  is  surrounded  by  and  incloses  areas  of  Laurentian  granite 
and  gneiss. 
Contacts  of  the  Laurentian  and  Huronian  rocks  are  described  for 
numerous  localities.  The  contacts  are  "generally  of  a  brecciated 
character,  the  gneisses  and  granites  while  in  a  plastic  condition  sur- 
rounding and  inclosing  the  Huronian  schists." 
The  Huronian  rocks  are  similar  in  many  respects  to  the  Keewatin 
series  of  the  Lake  of  the  Woods  and  Rainy  Lake  districts,  to  the 
south;  but  the  Huronian  of  the  area  under  discussion  includes  dark- 
blue  limestone  and  conglomerates  with  jasper  pebbles,  both  vrvy 
similar  to  those  of  the  typical  Huronian  area  north  of  Lake  Huron, 
and  the  rocks  are  accordingly  mapped  as  Huronian. 
The  Coutchiching,  supposed  by  Lawson  to  underlie  the  Keewatin 
of  the  Rainy  Lake  country,  is  possibly  here  represented  by  a  small 
area  west  of  Shallow  Lake,  mapped  as  Huronian.  However,  at  (till! 
Rock  Lake,  rocks  which  still  more  resemble  the  Coutchiching  of 
the  Rainy  Lake  region  are  found  to  be  but  highly  altered  Huronian 
beds  in  contact  with  the  Laurentian,  which,  when  followed  along  the 
strike,  take  on  the  general  aspect  of  the  remainder  of  the  Huronian 
of  the  district. 
Low,48  in  1897,  reports  on  his  explorations  of  the  Labrador  Penin- 
sula, along  the  Last  Main,  Koksoak,  Hamilton,  Manicuagan,  and  por- 
tions of  other  rivers.  Laurentian  rocks  occupy  nine-tenths  of  the 
area  of  the  peninsula.  They  include  gneisses  and  schi>t-.  some  of 
clastic  origin,  some  of  eruptive  origin.  The  clastic  portion  is  in 
nearly  all  cases  the  oldest. 
The  Huronian  rocks  comprise  beds  of  arkose,  conglomerate,  lime- 
stone, shale,  slate,  sandstone,  chert,  quartzite,  mica  schist,  and  erup- 
tives,  in  part  at  least  contemporaneous  with,  and  at  presenl  repre- 
sented by,  schists  characterized   by   chlorite,   epidote,   altered    horn 
