532  PRE- CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA 
of  the  Laurentian  and  Huronian  the  former  consists  of  a  coarse  quartz 
and  mica  rock,  while  the  first  rock  which  is  considered  Huronian  is  a 
dark-green,  highly  crystalline  hornblende  schist.  The  two  formations 
appear  as  usual  to  be  conformable.  Along  Manitounuck  Sound  is  an 
unaltered  stratified  series  in  which  no  fossils  were  found  and  which 
resemble  the  Nipigon  rocks.  These  are  called  the  Manitounuck  group. 
They  consist  mostly  of  siliceous  and  argillaceous  limestones,  sand- 
stones, quartzites,  shales,  ironstones,  amygdaloids,  and  basalts.  At 
Little  Whale  River  is  a  quartz  conglomerate  of  great  thickness  below 
these  rocks.  The  limestones  are  found  at  many  localities  at  the  base 
of  the  series.  They  have  a  cherty  concretionary  and  concentric  struc- 
ture. The  quartzites  and  sandstones  come  in  ascending  order.  Asso- 
ciated with  the  quartzites,  and  overlying  them,  is  a  series  of  cherts  and 
shales.  These  are  surmounted  by  a  great  thickness  of  amygdaloids  of 
various  kinds  and  of  diorites  of  a  basaltic  character.  At  Richmond 
Gulf  the  base  of  the  section  consists  of  sandstone  and  conglomerate, 
above  which  is  limestone  in  a  slightly  unconformable  position,  and  all 
is  capped  by  trap.  In  one  place  the  trap  rests  with  a  slight  uncon- 
formity upon  ferruginous  beds.  Spathic  iron  ore,  sometimes  of  con- 
siderable thickness,  is  in  places  interstratified  with  the  sandstone. 
Bell,32  in  1879,  reports  on  the  country  between  Lake  Winnipeg 
and  Hudson  Bay.  The  rocks  along  the  route,  with  the  exception  of 
one  Huronian  trough,  are  described  as  Laurentian  gneiss.  The  Hu- 
ronian rocks  belong  in  one  basin  or  trough,  conforming  with  the  gen- 
eral trend  of  the  Laurentian  gneiss  and  mica  schist.  Its  breadth  is 
about  14  miles  and  its  length  143  miles,  giving  an  area  of  about  2,000 
square  miles.  A  mica  schist  at  Pipestone  Lake  contains  different 
kinds  of  pebbles.  At  Seven-mile  Point  the  rock  is  a  micaceous  slate 
conglomerate,  the  pebbles  of  which  are  chiefly  of  gray  syenite.  At 
the  junction  of  the  Laurentian  and  Huronian  the  two  formations 
appear  as  usual  to  be  conformable  with  each  other.  The  last  of  the 
Laurentian  series  consists  of  gray,  coarse,  rough-surfaced  quartz  and 
mica  rock.  The  first  rock  on  what  is  considered  to  be  the  Huronian 
side  of  the  boundary  consists  of  highly  crystalline  dark-green  horn- 
blende schist,  ribboned  Avith  fine  lines  of  white  quartz  grains.  This 
schist  is  interstratified  with  bands  of  finely  ribboned,  slightly  cal- 
careous gray  gneiss.  i 
Bell,33  in  1880,  reports  on  explorations  of  the  Churchill  and  Nel- 
son River  and  around  Gods  and  Island  lakes.  The  Laurentian  gneiss 
is  the  prevailing  rock  throughout  the  whole  district  between  Knee 
and  Island  lakes.  The  stratification,  while  moderately  distinct,  is 
often  banded  and  contorted.  Its  average  texture  is  of  a  medium 
variety,  or  rather  tending  to  fine  grain,  but  coarse  forms  are  occa- 
sionally seen.  There  is  no  prevailing  or  general  direction  in  the 
strike  of  the  gneiss.    The  Huronian  rocks  occupy  a  series  of  troughs 
