'anhise.t  LAKE  SUPERIOR  REGION.  125 
liere  being  nowhere  an  abrupt  passage  from  one  class  to  the  other.  In 
ihe  passage  from  the  schists  to  the  gneisses  there  is  first  an  increase  in 
xequency  of  ramifying  veins,  then  lumps  of  gneiss  or  granite  in  the 
schists,  and  next  interstratification  of  the  schists  and  gneisses.  The 
conglomerate  at  Ogishki  Mauissi  lake,  which  attains  an  enormous  de- 
velopment and  contains  varieties  of  granitic  and  quartzose  bowlders,  as 
veil  as  flint,  jasper,  and  other  substances,  is  regarded  as  a  local  phase 
)f  the  schists,  as  the  bowlders  are  interbedded  with  the  flinty  argillites 
rad  sericite- schists.  The  entire  system  of  gneisses  and  schists  is  re- 
garded as  belonging  to  one  structural  system,  as  they  all  possess  a 
common  dip  and  pass  by  gradations  into  each  other.  The  iron-bearing 
'ocks  are  interlaminated  with  the  country  schists,  and  while  they  ex- 
libit  much  persistence,  they  do  not  persist  without  interruption.  In 
structure  the  region  is  a  simple  synclinal  fold,  the  strata  of  which  have 
i  thickness  of  106,204  feet.  The  succession  from  the  bottom  upward  is 
granite,  gneiss,  micaceous  and  hornblendic  schists,  gray  wacke,  argillite- 
schist  bearing  conglomerates,  and  sericitic  and  chloritic  schists  bearing 
ron  ores.  As  the  plainly  fragmental  rocks  grade  by  imperceptible 
stages  into  the  gneiss  and  granite,  the  whole  is  regarded  as  a  seclimen- 
;ary  series.  While  granite  pebbles  are  found  in  the  conglomerates, 
Ms  is  not  the  underlying  granite,  as  many  of  the  fragments  differ  in 
character  from  the  inferior  granite. 
Winchell  (N.  H.),175  in  1887,  gives  very  numerous  details  as  to  the 
geology  of  northeastern  Minnesota.  At  several  places  there  are  trail  si- 
ions  between  the  granite  gneiss  and  a  fine  grained  mica-schist.  In 
;he  syenite  are  sometimes  found  angular  fragments  of  micaschist.  The 
Vermilion  group  is  defined  as  including  the  lower  portion  of  the  corn- 
ilex  series  of  schists  designated  as  Keewatin  by  Lawson.  It  embraces 
;he  mica-schists  and  hornblende- schists  of  Vermilion  lake  and  their 
equivalents,  and  lies  between  the  gray wackes  on  the  one  side  and  the 
lasal  syenites  and  granites  on  the  other. 
The  iron  ores  of  Minnesota  are  at  three  horizons.  At  the  top  are  the 
itaniferous  ores;  which  are  associated  with  the  gabbro  and  constitute 
^hat  is  locally  known  as  Mayhew  Iron  range,  and  is  found  from  this 
•ange  at  many  points  all  the  way  to  Duluth.  The  nontitaniferous  mag- 
letic  ores  occur  at  several  localities  associated  with  hematite  ores  and 
ncluded  in  a  quartz-schist.  These  ores  are  comparable  to  those  of  the 
Penokee-Gogebic  Iron  range  on  the  south  side  of  lake  Superior,  and 
;hose  of  BlAgk  river  falls  in  Wisconsin.  Adjacent  to  Yermilion  lake  are 
lematite  orS^ssociated  with  jasper,  which  are  inclosed  in  a  schist,  the 
>edding  of  which  stands  vertical.  This  schistose  rock  is  probably  of 
gneous  origin,  and  in  its  relations  to  the  jasperoid  rocks  it  fills  all  t  heir 
cavities,  overlying  them  un conformably,  and  holding  fragments  of  the 
asper;  all  indicating  its  later  origin.  This  igneous  rock  passes  into 
ichlorite-schist,  and  this  into  the  sericite- schists  and  gray  wackes,  which 
;how  unmistakable  evidence  of  an  aqueous  arrangement.    The  jasper- 
