LAKE    SUPERIOR   REGION.  263 
the  more  compact  altered  schists  and  slates  only  in  its  rougher  sur- 
face of  fracture  and  a  somewhat  spotted  character.  The  greenstone 
conglomerates  of  Bigsby  resemble  roughly  fractured  pieces  of  diorite 
in  a  dioritic  paste.  The  quartzites  show  a  tendency  to  run  into  con- 
glomerates, and  certain  of  the  conglomerates  have  the  aspect  of.  a 
volcanic  breccia.  There  is  an  entire  absence  of  any  granitic  or 
gneissic  beds  in  the  conglomerates  and  breccias,  and  in  this  respect 
these  Huronian  rocks  differ  from  the  typical  area.  It  is  suggested 
that  this  fact  may  mean  that  the  formation  of  the  whole  Huronian 
series  took  place  subsequent  to  that  of  the  typical  Huronian,  and 
therefore  are  perhaps  more  nearly  equivalent  to  those  of  the  Quebec 
group.  The  granitoid  gneisses  and  intrusive  granites  are  universally 
cut  by  veins  of  red  orthoclase  feldspar  associated  with  quartz;  and 
basic  diorite  dikes  cut  both  the  granitic  and  the  altered  Laurentian 
rocks. 
Bell,2"58  in  1875,  describ  oxiore  of  Lake  Superior  the 
Laurentian,  Huronian,  ana  Upper  Copper-bearing  rocks.  The  Huron- 
ian occupies  a  large  extent  of  country,  alternating  with  bands  of  Lau- 
rentian, on  both  the  north  and  the  south  shores  of  the  lake.  North 
of  Lake  Superior  the  Laurentian  rocks  consist  for  the  most  part  of 
gray  and  reddish  gneiss,  with  micaceous  belts  and  mica  schists.  In 
the  same  region  the  Huronian  rocks  are  mostly  of  a  schistose  charac- 
ter, the  most  common  of  which  are  greenish  schists  and  imperfect 
gneisses,  which  include  micaceous,  hornblendic,  dioritic,  porphyrinic, 
siliceous,  cherty,  chloritic,  felsitic,  and  argillaceous  schists,  more  rarely 
dolomitic  schists,  and  occasionally  bands  of  magnetic  iron  ore  and 
hematite.  Connected  with  the  Huronian  rocks  are  various  patches  of 
granite  and  syenite  which  show  no  stratification.  In  the  Nipigon 
basin  the  Upper  Copper-bearing  rocks  have  their  maximum  develop- 
ment in  Canadian  territory.  The  basin  consists  of  marls  and  sand- 
stones, often  covered  with  trappean  outflows.  For  this  Upper  Cop- 
per-bearing series  the  term  Nipigon  group  is  proposed. 
Bell,239  in  1876,  finds  on  Lake  Winnipeg  extensive  areas  of  Lauren- 
tian gneiss  and  Huronian  schist.  The  run  of  the  stratification  is 
pretty  uniform,  averaging  from  50°  to  60°  south  of  east,  being  almost 
at  right  angles  to  the  general  strike  of  the  Laurentian  and  Huronian 
rocks  in  the  great  region  north  and  northwest  of  Lake  Superior. 
Bell,240  in  1877,  describes  the  rocks  from  the  head  of  Moose  River 
to  Michipicoten  and  Lake  Superior;  also  along  the  Goulais  River. 
Before  reaching  Lake  Superior  there  are  several  broad  alternating 
belts  of  Laurentian  gneiss  and  Huronian  schist.  The  Huronian  horn- 
blende and  mica  schists  are  cut  by  granite  veins  of  various  sizes,  one 
of  them  100  feet  thick.  On  Goulais  River  there  are  again  alternations 
of  Laurentian  and  Huronian  rocks. 
