210  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
They  consist  mostly  of  siliceous  and  argillaceous  limestones,  sandstones, 
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  structure. 
The  quartzites  and  sandstones  come  in  ascending  order.  Associated 
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  Kichmond  gulf  the 
base  of  the  section  consists  of  sandstone  and  conglomerate,  above  which 
is  limestone  in  a  slightly  unconformable  position  and  all  is  caj)ped  by 
trap.  In  one  place  the  trap  rests  with  a  slight  unconformity  upon  fer- 
ruginous beds.  Spathic  iron  ore,  sometimes  of  considerable  thickness, 
is  sometimes  interstratified  with  the  sandstone. 
Bell,3  in  1879,  reports  on  the  country  between  lake  Winnipeg  and 
Hudson  bay.    The  rocks  along  the  route,  with  the  exception  of  one  Hu- 
ronian  trough,  are  described  as  Lauren tian  gneiss.     The  Huronian  rocks \ 
belong  in  one  basin  or  trough,  conforming  with  the  general  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- con  glomerate,  the  pebbles! 
of  which  are  chiefly  of  gray  syenite.    At  the  junction  of  the  Lauren  tian] 
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  isj 
considered  to  be  the  Huronian  side  of  the  boundary  consists  of  highly] 
crystalline  dark  green  hornblende-schist,  ribboned  with  fine  lines  ofj 
white  quartz  grains.     This  schist  is  interstratified  with  bands  of  finely 
ribboned,  slightly  calcareous  gray  gneiss. 
Bell,4  in  1880,  reports  on  explorations  of  the  Churchill  and  Nelson 
river  and  around  God's  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  occasionally  seen.  There  is  no  pre- 
vailing or  general  direction  in  the  strike  of  the  gneiss.  The  Huronian 
rocks  occupy  a  series  of  troughs  in  several  localities.  The  rocks  are 
schist-conglomerate,  sometimes  garnetiferous,  steatite- schists,  green 
schists  and  felsite  schists,  most  of  them  being  more  or  less  calcareous. 
The  Laurentian  gneiss  occupies  the  area  between  the  Huronian  troughs. 
The  strike  of  the  Laurentian  gneiss  in  the  neighborhood  of  the  Huro- 
nian rocks  appears  in  most  cases  to  correspond  with  that  of  the  latter. 
Bell,5  in  1881,  reports  on  Hudson  bay  and  some  of  the  lakes  and 
rivers  lying  to  the  west  of  it.  Various  gneisses  and  schists  are  found 
at  different  points  which  are  referred  respectively  to  the  Laurentian  and 
