LAKE   SUPERIOR   REGION.  375 
bearing  formation  of  the  Vermilion  district  in  the  lower  Huronian, 
and  the  overlying  conglomerates,  Ogishke  and  Stnntz,  in  the  upper 
Huronian.  Later  work  resulted  in  the  assignment  of  the  iron  forma- 
tion, with  its  closely  associated  green  schists,  to  the  green  schist  por- 
tion of  the  basement  complex,  and  the  overlying  sediments  were 
assigned  to  the  lower  Huronian. 
The  succession  of  Grant,  N.  H.  Winchell,  H.  V.  Winchell,  and  Spurr 
of  the  Minnesota  Survey  for  the  Mesabi  district  was :  Keweenawan ; 
unconformity;  Animikie;  unconformity;  Upper  Keewatin;  possible 
unconformity ;  Lower  Keewatin.  Grant  recognized  in  the  "  Upper 
Keewatin  "  similarities  to  the  lower  Huronian  of  other  parts  of  the 
Lake  Superior  region,  although  it  was  not  discriminated  in  the  map- 
ping. Leith's  succession  differs  from  that  of  the  Minnesota  Survey 
in  the  discrimination  of  a  well-defined  sedimentary  series  beneath  the 
Animikie,  corresponding  roughly  to  Grant's  Upper  Keewatin,  and 
separated  by  a  marked  unconformity  with  the  basement  complex. 
His  succession  is:  Keweenawan;  unconformity;  Animikie  or  Upper 
Huronian;  unconformity;  Lower  Huronian;  unconformity;  Archean 
(includes  the  Keewatin  and  Laurentian).  Hall,  in  central  Minne- 
sota, finds  granites,  gneisses,  and  gabbros  of  the  basement  complex 
overlain  by  Huronian  quartzites  and  slates,  and  later  Leith  and 
Zapffe  mapped  here  a  great  series  of  upper  Huronian  slates  and  iron 
formation,  occupying  much  of  central  Minnesota,  and  correlated  the 
rocks  with  the  upper  Huronian  of  the  Mesabi  district. 
A  general  result  of  the  later  work  in  Minnesota,  and  particularly 
that  of  the  United  States  geologists,  Van  Hise,  Clements,  Bayley,  and 
Leith,  has  been  the  recognition  of  the  existence  of  large  areas  of 
Huronian  and  Keweenawan  granite  which  had  before  been  assigned 
to  the  Archean.  They  have  long  maintained  that  the  granites  of  the 
region  comprise  both  Archean  and  Huronian  granites,  and  that  it 
remains  for  detailed  mapping  to  indicate  the  relative  importance  of 
the  two.  The  Canadian  geologists  have  held  that  the  granites,  nearly 
all  of  which  they  have  mapped  as  Laurentian,  are  almost  entirely 
intrusive  into  the  Huronian  series.  In  this  they  are  followed  in  large 
part  by  the  Minnesota  geologists. 
Finally  the  joint  committee  of  the  Canadian,  Ontario,  United 
States,  and  Michigan  geological  surveys,  composed  of  Frank  D. 
Adams,  Robert  Bell,  A.  C.  Lane,  C.  K.  Leith,  W.  G.  Miller,  and 
Charles  R.  Van  Hise,  after  visiting  the  Marquette,  Gogebic,  Vermilion, 
Mesabi,  Rainy  Lake,  Lake  of  the  Woods,  Port  Arthur,  and  Lake 
Huron  districts  in  1904,  recognized  a  succession  for  the  entire  region 
identical  with  that  used  by  the  United  States  Geological  Survey  in  its 
mapping  in  Michigan  and  Minnesota,  Lawson's  Coutchiching  was 
found  to  be  essentially  above  rather  than  below  the  Keewatin  and  to 
belong  with  the  Huronian  series.     His  Keewatin  was  thought  to  be 
