204  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
The  iron  ores  of  Minnesota  are  at  three  horizons.  At  the  top  are 
the  titaniferous  ores,  which  are  associated  with  the  gabbro  and  consti- 
tute what  is  locally  known  as  the  Mayhew  iron  range,  and  which  are 
found  from  this  range  at  many  points  all  the  way  to  Duluth.  The 
nontitaniferous  magnetitic  ores  occur  at  several  localities  associated 
with  hematite  ores  and  included  in  a  quartz  schist.  These  ores  are 
comparable  to  those  of  the  Penokee-Gogebic  iron  range  on  the  south 
side  of  Lake  Superior,  and  those  of  Black  River  Falls  in  Wisconsin. 
Adjacent  to  Vermilion  Lake  are  hematite  ores  associated  with  jasper, 
which  are  inclosed  in  a  schist,  the  bedding  of  which  stands  vertical. 
This  schistose  rock  is  probably  of  igneous  origin ;  it  overlies  the  jas- 
peroid  rocks  unconformably,  filling  their  cavities  and  holding  frag- 
ments of  them — all  indicating  its  later  origin.  This  igneous  rock 
passes  into  a  chlorite  schist,  and  this  into  the  sericite  schists  and  gray- 
wackes,  which  show  unmistakable  evidence  of  an  aqueous  arrange- 
ment. The  jasperoid  hematite  is  a  sedimentary  rock,  not  an  erup- 
tive as  has  been  supposed  by  Wadsworth.  The  rock  was  not,  how- 
ever, deposited  in  its  present  condition.  The  beds  have  been  up- 
turned, folded,  crushed,  and  affected  by  intense  chemical  action.  The 
ore  is  regarded  as  a  result  of  chemical  or  metasomatic  change.  The 
general  succession  from  above  downward  is  as  follows :  (1)  Gabbro. 
(2)  Diabase  dolerite.  These  rest  unconformably  upon  the  lower  mem- 
bers. (3)  Reddish  gneiss  and  syenite,  which  includes  the  Misquah 
Hills,  White  Iron  Lake,  and  the  Giants  range  (Mesabi  Heights). 
This  is  a  case  of  a  fusion  of  sedimentary  beds  in  situ,  although  it  is 
not  generally  complete.  (4)  Graywacke,  sericite  schist,  argillite, 
quartzite,  and  jaspilite,  which  occur  about  Vermilion  Lake.  (5) 
Mica  schist,  hornblende  schist,  and  diorite — the  Vermilion  group. 
(6)  Mica  schist  and  granite  veined  with  syenite  and  granulite.  (7) 
Lower  syenites  and  gneisses,  generally  regarded  as  Laurentian.  Nos. 
3  to  7  are  conformable,  and  Nos.  4  to  7  graduate  into  one  another. 
There  is  reason  for  believing  that  the  Animikie  rocks  overlie  the 
greenstone  (2)  and  underlie  the  gabbro  (1)  of  the  above  succession. 
Winchell  (N.  H.),157  in  1888,  finds  the  Upper  Huronian  quartzites 
to  be  so  similar  to  those  of  Pipestone,  Cottonwood,  and  other  coun- 
ties in  Minnesota  that  the  former  are  regarded,  with  the  latter,  as 
Huronian.  The  Animikie  on  Gunflint  Lake,  while  not  found  in 
exact  superposition  on  the  Keewatin,  bears  such  relations  as  to  render 
it  probable  that  the  two  formations  are  discordant.  A  short  distance 
north  of  the  Animikie  the  Keewatin  rocks  are  found  with  a  dip  of 
80°,  and  these  a  little  farther  north  grade  conformably  into  the  crys- 
talline schists  of  the  Vermilion  group,  and  these  still  farther  north 
by  transition  pass  into  the  gneisses  and  syenites  of  the  Laurentian. 
The  Animikie  rocks  are  found  resting  uncomformably  on  the  gneiss 
west  of  Gunflint  Lake.     The  gabbro  is  observed  overlying  the  Anim- 
