LAKE  SUPERIOR  REGION.  131 
with  the  surrounding  schistose  mass.  Also  extensive  conglomeratic 
masses  are  found  full  of  granite  pebbles  of  large  size  in  sec.  2,  T.  48 
N.,  R.  26  W.,  and  in  sec.  29,  T.  48  N.,  R.  25  W.  In  opposition  to 
Brooks  it  is  maintained  that  there  is  but  one  Iron-group  formation. 
The  Quartzite  group  is  in  places  interstratified  with  ferruginous 
and  siliceous  seams,  as  well  as  novaculitic  strata  and  siliceous  lime- 
stones. Frequently  in  the  quartzite  is  a  conglomerate  containing 
abundant  quartz  fragments,  and  also  not  infrequently  containing 
granite  and  slate  fragments.  Oftentimes  these  conglomerates  contain- 
ing the  granite  fragments  are  very  close  to  the  massive  granite,  while 
it  not  infrequently  underlies  them.  At  one  place  in  which  the  quartz- 
ite is  in  contact  with  the  granite  the  one  rock  is  seen  to  graduate  by 
imperceptible  stages  into  the  other,  in  which  case  the  sedimentary 
strata  are  changed  into  the  granite-like  rock  by  being  exposed  to  the 
contact  with  the  eruptive  granite.  In  another  place  a  granite  breccia 
containing  large  fragments  of  granite  is  found  in  connection  with 
such  large  masses  of  granite  as  to  be  too  great  to  be  fragments  of  a 
breccia,  and  this  suggests  that  the  nucleus  of  the  hills  are  solid  gran- 
ites, whose  shattered  portions  are  recemented  on  the  spot  by  sedi- 
mentary debris  washed  into  the  interstices.  In  the  next  hill  to  the 
south  the  inclosed  water-worn  pebbles  are  in  part  granite  and  in  part 
slate.  Above  the  ore-bearing  rock  beds  is  generally  a  very  coarse 
quartzite  conglomerate  which  often  has  the  characters  of  a  coarse- 
grained ferruginous  quartzite  and  grades  down  into  a  brecciated  ore. 
The  fragments  are  chiefly  ore,  jasper,  and  quartz,  and  the  cement  is 
arenaceous  or  ferruginous.  This  occurrence  is  so  general  as  to  sug- 
gest that  great  disturbances  not  of  a  local  extent  must  have  occurred 
at  the  end  of  the  era  of  iron  sediments.  The  number  of  localities  and 
mines  at  which  this  conglomerate  or  breccia  occurs  is  very  great. 
Among  the  latter  are  the  Home,  Gibbon,  Jackson,  Cleveland,  Cas- 
cade, Gribben,  Salisbury,  Lake  Superior,  Champion,  Saginaw  and 
Goodrich,  Keystone,  Republic,  and  Michigamme. 
The  Iron  group  occupies  a  position  inferior  to  the  Quartzite  group, 
and  there  are  not  hvo  horizons  here,  as  supposed  by  Brooks.  It  is 
composed  of  banded  jasper,  conformable  chlorite  schist,  and  ore.  The 
ore  deposits  are  not  regular  sedimentary  layers,  but  the  product  of  the 
decomposition  of  the  impure  ledges  by  percolating  waters  leaching 
out  the  siliceous  matter  and  replacing  it  with  iron  oxide1,  and  are 
therefore  very  irregular  in  form.  The  strata  are  in  a  much  disturbed 
condition,  folded  and  distorted  in  every  possible  way.  usually  without 
faults.  These  disturbed  beds  lie  in  every  instance  directly,  but  often 
unconformably,  on  chloritic  or  hydromicaceous  schists,  or  on  crystal 
line  dioritic  masses,  which  are  constant  associates  of  the  chlorite 
schists,  or  on  dioritic  schists.  At  the  Jackson  mine  are  knobs  of 
diorite  associated  with  schists  surrounded  by  the  banded  jasper  rocks 
