LAKE   SUPERIOR  REGION.  207 
and  argillite  group;  (2)  Marquettian  system,  27,500  feet  thick,  in- 
cluding the  Ogishki  group,  10,000  feet  thick,  the  Tower  group 
(earthy  schists),  15,000  feet  thick,  and  the  graywacke  group,  2,500 
feet  thick;  (3)  Laurentian  system,  89,500  feet  thick,  including  the 
Vermilion  group,  more  than  1,500  feet  thick,  and  the  gneissic  group, 
more  than  88,000  feet  thick.     Total,  more  than  121,082  feet. 
Winchell  (H.  V.),159  in  1888,  gives  detailed  observations  about 
many  localities  in  northeastern  Minnesota.  The  mica  schist  and  in- 
terbedded  gneiss  are  cut  by  granite  veins  at  numerous  places. 
Hall  (C.  W.),100  in  1889,  describes  the  distribution  of  the  granites 
of  the  Northwestern  States,  and  particularly  those  of  Minnesota. 
They  are  found  to  be  either  intrusive  or  granitic  veinstones,  the 
latter  being  insignificant  in  quantity.  The  granites  of  Minnesota 
as  to  age  are  probably  later  than  the  Laurentian  floor  of  the  conti- 
nent, but  earlier  than  the  close  of  the  Agnotozoic  era.  There  are 
three  or  four  grand  periods  of  eruptive  activity. 
Winchell  (N.  H.),161  in  1889,  gives  a  summary  of  the  results  of 
work  on  the  crystalline  rocks  of  northeastern  Minnesota.  In  many 
points  the  conclusions  and  facts  are  the  same  as  in  the  previous  re- 
ports. The  Laurentian  age  is  made  to  include  the  gneiss,  granite,  and 
syenite,  but  excludes  the  crystalline  schists.  It  is  the  fundamental 
gneiss  of  Minnesota.  Associated  with  this  fundamental  gneiss  are 
areas  of  massive  eruptive  syenite  which  are  regarded  as  due  to  the 
hvdrothermal  fusion  of  the  gneissic  belts.  The  gneisses  grade  into 
the  Vermilion  schists,  which  are  the  equivalent  of  Lawson's  Coutchi- 
ching.  Along  their  contact  the  Laurentian  plays  the  part  of  in- 
trusive rocks,  which  is  indicative  that  the  opening  of  Vermilion  age 
was  one  of  violent  volcanic  action.  The  beds  have  subsequently  been 
affected  by  hydrothermal  fusion,  which  has  tended  to  unify  the  Lau- 
rentian and  Vermilion  systems. 
The  Vermilion  group  passes  by  conformable  transition  into  the 
KeeAvatin.  The  character  of  the  Keewatin  rocks  indicates  that  there 
was  active  volcanic  action  during  the  wdiole  period  and  that  the  ejecta- 
menta  were  received  and  distributed  by  the  waters  of  the  surround- 
ing sea.  This  is  indicated  by  the  alternation  of  breccias  and  volcanic 
material  with  truly  sedimentary  strata.  The  Keewatin  is  the  iron- 
bearing  formation.  The  iron  ore  is  associated  with  the  jaspilite, 
which  is  of  sedimentary  origin.  Parallel  with  the  Keewatin  of 
Minnesota  is  the  serpentine  and  dioritic  group  of  Rominger  in  the 
Marquette  region.  Above  this  group  in  both  regions  is  a  profound 
unconformity. 
The  Animikie  series  of  Minnesota,  bearing  iron  at  one  horizon,  is 
the  equivalent  of  the  Marquette  series  bearing  the  iron  group  of 
Rominger,  of  the  Penokee-Gogebic  series  of  Michigan  and  Wiscon- 
sin, of  the  Mesabi  range  in  Minnesota,  of  the  Black  River  iron-bear- 
