LAKE    SUPERIOR   REGION.  201 
posits  bear  the  same  relations  to  the  granite  as  do  those  of  Mesabi, 
and  they  are  regarded  as  the  same  formation. 
Winchell  (N.  H.), 150  in  1884,  gives  the  general  succession  of  rocks 
in  northeastern  Minnesota,  in  descending  order,  as  follows:  (1)  Pots- 
dam, including  the  Keweenawan  sandstones,  shales,  and  conglomer- 
ates, changed  by  igneous  gabbros  and  dolerites  locally  to  red  quartz- 
ites,  felsites,  quartz  porphyries,  and  red  granites.  (2)  Taconic 
group,  including  the  Animikie  series,  the  Gunflint  beds,  the  Mesabi 
iron  rocks,  the  Ogishki  Manissi  conglomerate  (?),  the  Thompson 
slates  and  quartzites,  and  the  Vermilion  iron  rocks.  (3)  Huronian 
group  (?),  including  magnesian  soft  schists,  becoming  syenitic  and 
porphyritic,  found  on  the  north  side  of  Gunflint  Lake,  along  the 
national  boundary,  and  at  Vermilion  Lake.  (4)  Montalban  (?),  in- 
cluding mica  schists  and  micaceous  granites  about  Vermilion  Lake 
and  on  Mississippi  River.  (5)  Lauren tian,  including  massive  horn- 
blende gneiss  and  probably  the  Watab  and  St.  Cloud  granites.  This 
succession  is  parallelized  with  those  of  other  writers  given  for  the 
Northwestern  States. 
Winchell  (N.  H.)  and  Upham,151  in  1884  and  1888,  give  detailed 
geological  maps  and  descriptions  of  many  of  the  counties  of  Minne- 
sota, which  include  the  Laurentian  gneisses  and  granites  of  Missis- 
sippi and  Minnesota  rivers,  the  slates  of  the  upper  Mississippi,  and 
the  quartzites  and  conglomerates  of  Cottonwood,  Pipestone,  Rock, 
Brown,  and  Nicollet  counties,  which  are  regarded  as  Potsdam  sand- 
stone. The  copper-bearing  traps  and  conglomerates  of  Chisago  and 
Pine  counties  are  placed  as  Lower  Cambrian.  These  reports  contain 
nothing  as  to  structural  relations  not  found  in  the  annual  reports. 
Winchell  (N.  H.),152  in  1885,  finds  between  Two  Harbors  and  Ver- 
milion Lake  two  rock  ranges,  the  first  being  Mesabi  proper  and  the 
second  the  Giants  range.  Resting  unconformably  upon  the  syenites 
of  the  Giants  range  are  the  Huronian  conglomerates  and  greenstones 
of  Vermilion  Lake,  while  south  of  this  range  are  the  slates  and  quartz- 
ites of  the  Animikie,  overlain  by  the  gabbro  and  red  granite  of  the 
Mesabi  range,  which  is  in  turn  overlain  by  the  trap  rocks  of  the 
Cupriferous  series.  The  Huronian  is  represented  as  resting  conform- 
ably below  the  Animikie,  although  not  appearing  at  the  surface. 
There  are  three  iron-ore  horizons — the  titanic  iron  of  the  gabbro  belt, 
the  iron  ore  of  the  Mesabi  range  belonging  in  the  Animikie,  and  the 
hematite  of  the  Vermilion  mines,  which  seems  to  be  the  equivalent  of 
the  Marquette  and  Menominee  iron  ores. 
Winchell  (N.  H.),15:i  in  1885,  divides  the  crystalline  rocks  of  the 
northwest  into  six  groups,  in  descending  order:  (1)  A  granitic  and 
gabbro  group,  which  is  a  part  of  living's  Cupriferous,  and  is  by  Hunt 
parallelized  with  the  Montalban.  It  includes  rocks  which  have  passed 
for  typical  Laurentian,  while  the  gabbros  are  eruptive  and  are  like  the 
