LAKE    SUPERIOR   REGION".  133 
north  of  the  Felch  Mountain  ore  formation  are  found  to  be  absolutely 
identical.  The  dioritic  rocks  are  found  generally  and  play  the  part 
of  an  intrusive  with  regard  to  the  strictly  sedimentary  rock  beds  of 
the  Huronian  series.  The  Dioritic  group  is  held  to  be  older  than  the 
Iron  group  because  it  exhibits  a  greater  degree  of  metamorphism 
and  on  the  ground  that  it  is  lithologically  like  the  equivalent 
Dioritic  group  of  the  Marquette  district.  It  has  evidently  been  trans- 
formed under  the  cooperation  of  heat  and  partially  brought  into  a 
plastic  condition. 
In  the  eastern  part  of  the  Menominee  region  the  rocks  found  com- 
prise, in  descending  order,  the  Lake  Hanbury  slate  group,  perhaps 
2,000  feet  in  thickness;  the  Quinnesec  ore  formation,  which  comprises 
micaceous  and  argillitic  strata  containing  ore  bodies,  not  less  than 
1,000  feet  thick,  and  the  Norway  limestone  belt,  at  least  1,000  feet 
thick.  The  Commonwealth  mine,  in  the  western  part  of  the  Menom- 
inee district,  represents  a  higher  horizon  than  the  Quinnesec  ore 
formation. 
Rominger,44  in  a  report  of  the  Michigan  Survey  for  1881  to  1884 
(published  in  1895),  further  discusses  the  complex  described  in  the 
former  volume  as  the  Huronian  system.  The  lower  granite  and 
gneissoid  portion  of  the  rock  groups  in  the  Marquette  region  ex- 
hibits the  characters  of  an  eruptive  and  not  of  an  altered  sedimentary 
rock.  Generally  a  solid  crust  of  granite  probably  served  as  a  sub- 
stratum on  which  the  Huronian  sediments  were  laid  down,  but  an 
opportunity  is  not  often  afforded  to  see  the  rocks  in  contiguity  well 
enough  exposed  to  alloAV  a  discrimination  as  to  whether  such  contact 
is  an  original  primary  one  or  resulted  from  dislocation.  The  exist- 
ence of  granite  as  a  surface  rock  at  the  time  the  Huronian  sedi- 
ments formed  is  proved  by  the  occurrence  of  belts  of  granite,  con- 
glomerate, and  breccia  in  different  horizons  of  the  series. 
A  large  belt  of  conglomerate,  formed  of  rounded  weather-worn 
granite  pebbles  and  schistose  rock  fragments,  cemented  by  a  matrix 
of  similar  schistose  material,  is  seen  in  contact  with  a  granite  belt  in 
the  south  half  of  sec.  2,  T.  48  N.,  R.  26  W. ;  in  the  SE.  \  sec.  22.  T. 
47  X.,  R.  26  W.;  and  in  the  north  half  of  sec.  21),  T.  48  X..  R.  25  W. 
In  the  first  of  these  localities  the  fragments  are  different  from  the 
underlying  granite.  The  second  locality  furnishes  a  better  proof  of 
the  deposition  of  Huronian  sediments  on  a  base  of  granite.  Here 
several  knob-  centrally  composed  of  massive  granite  are  surrounded 
by  a  mantle  of  coarse  granite  breccia,  with  a  well-laminated  quart- 
zose  material  as  a  cement.  This  breccia  is  conformably  succeeded 
by  hydromica  slates,  interlaminated  with  heavy  belts  of  compacl 
quartzite.  At  the  third  locality  granite  conglomerate  is  interlami- 
nated with  dioritic  schists,  but  is  remote  from  granite  outcrops.  The 
gradation  of  the  quartzite  formation  into  the  granite,  described  in  the 
