LAKE    SUPERIOR    REGION.  137 
than  the  Eastern  Potsdam  sandstone;  that  it  was  upturned,  faulted 
along  the  escarpment,  and  much  eroded  before  the  deposition  of  the 
Eastern  sandstone;  that  the  latter  was  laid  down  unconformably 
against  and  upon  the  former,  and  that  subsequent  minor  faulting  along 
the  old  line  ensued,  disturbing  the  contact  edge  of  the  sandstone. 
Fulton,47  in  1888,  describes  the  Huronian  rocks  of  the  eastern  Me- 
nominee region  as  consisting  of  three  formations.  The  basal  forma- 
tion is  a  crystalline  siliceous  limestone  at  least  1,200  feet  thick,  which 
outcrops  at  many  localities  along  the  range,  especially  north  of  the 
Norway,  Quinnesec,  and  Chapin  mines.  The  next  group,  estimated 
at  a  thousand  feet  in  thickness,  is  the  Quinnesec  ore  formation.  It 
consists  of  siliceous  or  jasper  slates,  largely  impregnated  with  iron 
oxides.  These  are  succeeded  by  argillaceous  hydromica  slates  and 
flesh-colored  slates.  This  formation  embraces  the  deposits  of  iron 
ore.  The  third  formation  is  a  series  of  dark-gray,  slaty,  or  schistose 
rocks,  with  occasional  quartzose  bands,  having  a  thickness  of  2,000 
feet,  and  is  called  the  Lake  Hanbury  slate  group.  Detailed  sections 
at  the  East  Vulcan,  Curry,  Norway,  Cyclops,  and  Quinnesec  mines 
are  described.  In  some  cases  the  ore  is  associated  with  the  Potsdam 
sandstone,  which  rests  unconformably  in  a  horizontal  position  upon 
the  flexed  and  denuded  Huronian  rocks.  The  iron-ore  beds  in  the 
Huronian  are  generally  associated  with  aluminous  slates  or  soap- 
stones. 
Winchell  (N.  H.),48  in  1888,  describes  the  conglomerate  overlying 
the  ore  and  jasper  formation  at  several  mines  in  the  Marquette  dis- 
trict, and  places  the  overlying  quartzite  in  the  Potsdam.  North  of 
Bessemer  is  a  basal  conglomerate  of  the  cupriferous  series  which  is  in- 
ferred to  lie  unconformably  upon  the  Gogebic  iron-bearing  rock. 
This  conglomerate  appears  to  be  the  equivalent  of  the  overlying  Pots- 
dam conglomerate  of  the  Marquette  region,  which  makes  the  Gogebic 
series  pre-Potsdam.  The  granite  underlying  the  Huronian  slates  at 
the  Aurora  mine  was  originally  a  conglomerate,  but  it  has  acted  the 
role  of  an  eruptive  rock  and  has  flowed  over  the  adjoining  sedimen- 
tary strata.  This  granitic  conglomerate  is  parallelized  with  the 
Ogishki  conglomerate  of  Minnesota,  and  the  overlying  sedimentary 
rocks  are  the  equivalent  of  the  Animikie. 
Winchell  (Alexander)  ,49  in  1888,  finds  the  Marquette  iron-1  >ea  ring 
rocks  to  have  the  same  geological  position  witli  respect  to  the  crystal- 
line schists  and  gneisses,  and  to  consist  of  sediments  of  the  same  char- 
acter, as  those  of  the  Vermilion  range.  At  Deer  Lake  furnace  is  a 
peculiar  conglomeratic  rock  which  appears  to  be  sedimentary,  but  is 
much  altered  and  has  a  quasi-eruptive  aspect.  This  conglomerate  is 
like  that  of  Stuntz  Island,  in  Vermilion  Lake.  Near  Negaunee  is  an 
argillite  which  has  a  lower  dip  than  a  greenish  chloride  quartzose 
