LAKE   SUPERIOR   REGION.  373 
ronian  greenstones;  green  schists  and  iron  formation;  Lauren tian 
granites  and  gneisses  intruding  upper  and  lower  Huronian.  This 
is  really  the  succession,  except  as  to  names,  of  the  United  States  Geo- 
logical Survey  for  this  district,  their  upper  Huronian  corresponding 
with  the  United  States  Geological  Survey's  lower  Huronian,  and 
their  lower  Huronian  corresponding  with  the  green  schist  portion  of 
the  basement  complex  now  called  Keewatin.  They  differ  from  the 
United  States  Geological  Survey  in  not  recognizing  the  presence  on 
the  north  shore  of  granites  and  gneisses  older  than  the  sedimentary 
Huronian,  holding  all  the  granites  and  gneisses  to  be  intrusives. 
Alexander  Winchell's  succession,  based  principally  on  Minnesota 
studies,  is:  Keweenawan,  Huronian,  Keewatin,  Vermilion,  Lauren- 
tian.  At  the  base  of  the  Huronian  is  a  great  structural  break.  The 
three  lower  series  are  in  conformity  and  grade  into  one  another. 
This  is  much  the  same  as  this  part  of  the  succession  given  by  N.  H. 
Winchell,  except  that  one  great  formation,  the  Ogishki  conglomerate, 
is  placed  by  the  latter  as  a  part  of  the  Animikie  (Huronian),  while  by 
Alexander  Winchell  it  is  placed  with  the  Keewatin. 
N.  H.  Winchell's  succession  is:  Keweenawan;  Animikie;  Norian; 
Pewabic  quartzite  (all  of  which  are  included  in  the  "  Taconic  ")  ; 
Keewatin ;  Vermilion ;  Laurentian  (which  are  included  in  the  Archean 
or  "Azoic  ") .  The  Keweenawan  is  doubtfully  called  Potsdam,  and  is, 
with  the  Animikie,  placed  as  the  "Georgia  formation;"  and  the 
Pewabic  quartzite  is  provisionally  placed  with  the  "Potsdam  granular 
quartz."  Included  in  the  "  Taconic  "  are  the  quartzites  of  Minnesota, 
Iowa,  Dakota,  and  Wisconsin.  The  part  of  the  succession  placed  in 
the  "  Taconic  "  differs  from  Irving's  succession  for  this  part  of  the 
column  in  that  the  formations  which  Winchell  includes  in  the 
"  Norian  "  and  Pewabic  are  regarded  as  the  great  basal  gabbro  mass 
of  the  Keweenawan,  between  the  upper  Keweenawan  and  the  Anim- 
ikie instead  of  below  the  Animikie.  It  is  not  necessary  to  say  that 
Irving  regarded  all  of  these  members  as  pre-Cambrian.  The  succes- 
sion within  the  Archean  is  the  same  as  that  of  Lawson,  the  difference 
being  only  that  "  Vermilion "  is  substituted  for  "  Coutchiching." 
Later  he  used  the  term  "  Coutchiching."  Also  the  Keewatin  elastics, 
"  Vermilion  "  schists,  and  Laurentian  gneiss  are  regarded  as  in  com- 
plete conformity,  all  detrital,  and  the  lower  members  but  more  meta- 
morphosed than  the  upper. 
In  a  later  classification  N.  H.  Winchell  included  in  the  "  Taconic  " 
the  Keweenawan  and  Animikie;  in  the  Archean,  "Upper"  and 
"  Lower "  Keewatin,  separated  by  unconformities.  The  Pewabic 
quartzite  also  was  placed  with  the  Keewatin,  but  was  not  assigned  to 
either  of  the  main  divisions.  His  Lower  Keewatin  includes  rocks 
which  the  United  States  Geological  Survey  has  referred  to  the  base- 
ment complex  and  lower  Huronian.     The  same  is  true  of  his  Upper 
