lf>8  PRE-CAMBRIAN    ROCI^S    OF    NORTH    AMKRTOA.  \nvu..W. 
Laurentian,  believing  this  part  to  be  of  later  age  and  intrusive.  Daw- 
son about  the  lake  of  the  Woods  made  the  same  discrimination. 
Irving,  in  bis  lafer  work,  differed  from  those  who  preceded  him  in  that 
he  included  in  the  Laurentian  all  the  thoroughly  crystalline  schists, 
with  some  of  the  obscure  green  schist-conglomerates;  that  is,  he  placed 
as  a  part  of  the  Laurentian  a  large  group  of  finely  schistose  rocks  cut 
by  granite  veins  which  had  heretofore  been  taken  to  be  greatly  meta- 
morphosed detrital  material  and  had  been  placed  in  the  Huronian.  He 
also  regarded  as  belonging  here  many  of  the  fine  grained  crystalline 
schists  of  a  similar  character  ou  the  north  shore,  placed  by  the  earlier 
Canadian  geologists  with  the  Huronian.  For  this  Laurentian  increased 
in  magnitude  he  used  the  term  Archean.  Lawson  and  the  Profs. 
Winchell  use  the  term  Laurentian  to  cover  practically  the  same  class 
of  rocks  as  the  earlier  Canadian  geologists,  although  Lawson  differs 
from  them  in  regard  to  their  origin  and  age.  It  was  early  remarked 
by  Macfarlane  and  later  by  Whittlesey,  Brooks  and  Kominger  that  the 
Laurentian  of  lake  Superior  differs  from  that  system  in  eastern  Canada 
in  containing  no  limestones,  quartzites,  iron  ores,  or  other  rocks  of  the 
plainly  detrital  class.  Brooks  and  Chamberlin  remark  that  it  is 
doubtful  whether  the  lake  Superior  Laurentian  is  the  equivalent  of  the 
eastern  Laurentian  of  Canada. 
The  lake  Superior  Huronian  of  the  larger  number  of  the  Canadian 
geologists  includes  the  quartzites,  slates,  fine  grained  green  schists, 
all  of  which  are  sometimes  conglomeratic,  and  the  pebbles  often  dis- 
torted and  metamorphosed.  It  also  includes  the  mica-schists,  horn- 
blende-schists and  fine  grained  gneisses  bearing  calcite,  with  certain 
ferruginous  schists  and  basic  and  acid  volcanic  products.  The  attitude 
of  the  Huronian  schists  is  either  vertical  or  steeply  inclined.  The  Ani- 
mikie  is  not  included  in  the  Huronian.  On  the  south  shore  Brooks  and 
Pumpelly  in  their  earlier  work  included  in  the  Huronian  all  the  rocks 
in  character  like  those  placed  in  this  system  on  the  north  shore,  with 
also  large  areas  of  rocks  the  clastic  character  of  which  is  evident,  such 
as  limestones,  ferruginous  beds,  slates,  graywackes,  etc.,  which  while 
always  tilted  or  gently  folded  have  not  the  schistose  structure  of  the 
Huronian  of  the  north  shore,  but  rather  resemble  the  Animikie.  Later? 
Brooks  placed  as  the  upper  member  of  the  Huronian  large  areas  of 
gneiss  and  granite  which  had  earlier  been  regarded  as  Laurentian. 
Rominger  went  a  step  farther  and  recognized  in  his  published  report 
ou  the  south  shore  the  Huronian  only,  seeing  as  he  did  that  a  part  of 
the  granite-gneiss  certainly  cuts  a  portion  of  the  schistose  rocks  which 
had  been  regarded  as  Huronian.  He  thus  included  in  the  Huronian 
the  granite-gneisses  which  are  equivalent  to  Lawson's  Laurentian,  and 
reverted  to  the  position  of  Foster  and  Whitney,  making  his  Huronian 
the  equivalent  of  their  Azoic,  one  indivisible  system.  In  Eominger's 
later  unpublished  manuscript  he,  however,  distinctly  recognizes  besides 
a  later  intrusive  granite  an  earlier  granite  gneiss  upon  which  the  lowest 
