146  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
Pumpelly  and  Van  Hise,59  in  1891  and  1892,  find  that  in  places 
the  ore  formation  of  the  Menominee  and  Felch  Mountain  districts 
passes  down  into  the  limestone.  In  the  deeper  workings  of  the 
Chapin  the  ores  resting  almost  directly  upon  the  limestone  are  found 
to  bear  a  considerable  percentage  of  carbonates,  including  iron,  cal- 
cium, and  magnesium.  The  Metropolitan  ore  deposits  in  the  Felch 
Mountain  district  are  found  associated  with  or  within  the  limestone. 
At  one  pit  the  ore  and  jasper  may  be  seen  interlaminated  with  and 
grading  down  into  a  limestone.  It  is  therefore  probable  that  the  ore 
formation  of  these  districts,  in  part  at  least,  is  but  an  upward  con- 
tinuation of  the  limestone  formation,  perhaps  differing  from  it  origi- 
nally only  in  that  the  upper  part  contained  a  greater  quantity  of 
original  carbonate  of  iron. 
Above  the  ore  formation  at  Quinnesec  test  pits  show  the  presence 
of  a  typical  chert  and  jasper  conglomerate,  in  every  respect  like  the 
basement  conglomerates  of  the  Upper  Marquette. 
Van  Hise,60  in  1892,  describes  the  Huronian  volcanics  south  of 
Lake  Superior.  These  include  both  lavas  and  tuffs  interstratified 
with  each  other  and  with  contemporaneous  elastics.  Among  the  lavas 
are  amygdaloids,  the  amygdules  of  which  are  in  certain  cases  jasper 
similar  to  that  of  the  iron  formation  adjacent,  and  are  believed  to 
have  been  formed  at  the  same  jasper- forming  period.  The  volcanics 
are  much  more  altered  than  those  of  the  Keweenawan.  They  are 
found  in  various  places,  but  the  most  extensive  areas  are  in  the 
Gogebic  district  west  of  Gogebic  Lake  and  in  the  Michigamme  dis- 
trict north  of  Crystal  Falls.  In  the  first  locality  the  series  is  7,000 
or  8,000  feet  in  thickness.  This  great  mass  of  material  was  piled  up 
while  to  the  west  TOO  to  800  feet  of  the  sediments  of  the  iron-bear- 
ing formation  were  accumulating.  In  this  district,  therefore,  at  the 
same  time  there  were  being  deposited  the  ordinary  sediments  of  the 
area  and  locally  a  volcanic  series  of  a  wholly  different  character. 
Lane,01  in  1892,  holds  that  certain  of  the  ore  bodies  of  the  Mar- 
quette district  are  produced  by  abstracting  iron  oxide  from  amphib- 
olites  and  depositing  this  material  at  other  places.  The  water  is 
regarded  as  upward  moving,  hence  the  ore  bodies  rest  upon  the 
diorites  as  foot  walls.  It  is  not  denied  that  in  other  places  the  iron 
is  derived  from  a  carbonate,  or  that  silica  is  replaced  by  the  iron 
oxide.  At  the  Volunteer  mine  the  ore  seems  in  part  to  have  replaced 
the  sandstone. 
Wads  worth, C2  in  1893,  gives  a  sketch  of  the  iron,  gold,  and  copper 
districts  of  Michigan.  The  Azoic  or  Archean  rocks  are  divided  from 
the  base  upward  into  the  Cascade,  Republic,  and  Holyoke  forma- 
tions. These  divisions  are  placed  in  order  as  equivalent  to  the  funda- 
mental complex,  Lower  Marquette  series,  and  Upper  Marquette  series 
of  Van  Hise.     They  are  unconformable  and  represent  three  different 
