164  PRE-CAMBRjAN    ROCKS    OF    NORTH    AMERICA.  [mm    86. 
Brooks,  Pumpelly,  Irving,  Chamber lin,  Sweet,  and  Wright  recognize 
about  the  same  general  succession;  lake  Superior  sandstone;  unco] 
formity;  Keweehawan;  unconformity;  then  a  great  system  of  roclj 
included  in ,  the  Huroni  an;  another  unconformity;  and  then  a  complex 
of  granites,  gneisses  and  schists.  Irving  in  his  later  work  separates 
from  the  Huronian  and  puts  in  the  Laurentian  the  formation  of  dioritjj 
schists,  obscure  green  conglomerates,  chloritic  schists,  etc.,  cut  hy 
granite  veins  in  the  Marquette  district,  which  Brooks  placed  as  tffl 
lowest  part  of  the  Huronian,  but  the  relations  of  which  are  said  not  tc 
have  been  fully  made  out.  There  is  the  further  resultant  ditf'ereneji 
between  Brooks  and  Irving  that  Brooks  regards  very  considerable 
masses  of  granite  in  the  Menominee  district  as  the  highest  member  ol 
the  Huronian.  As  this  granite  is  said  to  overlie  conformably  the  Flu 
Ionian  schists  and  to  send  dikes  into  them,  it  is  suggested  that  toward 
the  end  of  the  Huronian  period  there  was  a  great  eruptive  outflow  o|i 
granite.  As  has  been  seen,  these  facts  are  explained  by  Irving  by 
excluding  from  the.  Huronian  the  granite  and  the  schists  cut,  althouglij 
it  is  recognized  that  lesser  granitic  intrusions  have  occurred  since  Hu|| 
ronian  time. 
Rominger,  in  his  earlier  work  on  the  south  shore,  seeing  that  his  dm 
ritic  group  of  Huronian   locks  is  cut  by  granite,  and  considering  thei 
former  as  a  sedimentary  rock,  and  finding  also,  as  he  believed,  actuaji 
transitions  between  the  fragmental  quartzites  and  granites,  placed  tliji 
whole  complex  as  Huronian  and  regarded  the  granite  as  the  youngest 
member.     These  positions  are,  however,  very  largely  abandoned  in  his 
later  unpublished  work.     The  existence  of  granite  and  gneiss  prior  to 
the  deposition  of,  and  which  have  yielded  debris  to,  the  lowest  member! 
of  the  Huronian,  is  recognized,  although  contacts  are  said  to  be  nil 
often  sufficiently  frequent  to  enable  a  eliscrimination  to  be  made  be< 
tween  the  original  primary  granites  and  gneisses  and  those  of  latei 
eruptive  origin.     The  recomposed  character  of  the  detrital  rocks  whicl 
repose  upon  and  have  derived  debris  from  the  granites  and  gneisses 
instead  of  grading  into  them,  is  now  seen.     It  is,  however,  still  maim 
tained  that  the  great  mass  of  the  grauite  and  gneiss  is  an  eruptive  qjii 
later  age  than  the  detrital  rocks.     The  dioritic  group,  which  is  so  frei 
quently  cut  by  granite  veins,  before  considered  as  the  bottom  of  tin  j 
Huronian,  is  recognized  as  an  igneous  rock  which  must  be  excludec  ] 
from  the  sedimentary  series.     Romingers  succession  is,  then,  lake  S*tu] 
perior   sandstone;    unconformity;    Keweenawan;    unconformity;    Hu 
ronian  sedimentary  series,  which  has,  however,  been  disturbed  by  grea' 
intrusions  of  granite  and  gneiss,  with  also  basic  rocks;  unconformity 
granite- gneiss- schist  complex. 
It  is  therefore  to  be  noted  that  Brooks,  Irving,  and  Kominger,  wh( 
have  done  the  most  work  in  the  detailed  mapping  of  the  rocks  of  th< 
south  shore,  reach  an  identical  conclusion  as  to  the  succession,  the  onfl 
difference  being  one  of  emphasis.     Kominger  insists  on  the  great  impor 
