138  "  PRE-CAMBR1AN    GEOLOGY    OF    NORTH    AMERICA. 
rock  across  a  railroad  from  it,  and  the  two  are  therefore  uncon- 
formable. 
The  rocks  of  Marquette  are  older  than  the  Huronian,  because  they 
differ  from  them  lithologically;  because  the  Canadian  Huronian  is 
immediately  succeeded  by  the  Paleozoic  system,  while  the  Marquette 
strata  are  not ;  because  some  evidences  are  found  that  in  the  Mar- 
quette district  there  is  an  overlying  unconformable  sub-Paleozoic  sys- 
tem, and  because  the  Marquette  series,  being  the  equivalent  of  the 
Vermilion,  is  older  than  the  Animikie  slates,  which  are  the  equivalent 
of  the  Huronian. 
The  rocks  of  the  Gogebic  range  are  regarded  as  the  equivalent  of 
those  of  the  Marquette  region  because  they  resemble  them  lithologic- 
ally and  because  they  are  in  an  analogous  position  to  the  crystalline 
rocks.  Between  the  Penokee  series  and  the  underlying  schists  there 
is  a  marked  unconformity,  the  Penokee  rocks  dipping  to  the  north, 
while  the  hornblende  schists  dip  to  the  south.  The  Penokee  series 
strata  are  lithologically  unlike  the  ore-bearing  strata  of  the  Gogebic, 
Marquette,  and  Vermilion  regions,  but  resemble  those  of  the  Animikie 
series  and  are  therefore  perhaps  Huronian,  while  the  Gogebic  iron- 
bearing  strata  are  not. 
Merriam,50  in  1888  and  1889,  in  a  detailed  systematic  study  of  parts 
of  the  Marquette  district,  ascertained  that  about  many  of  the  masses 
of  basic  eruptives  the  clastic  rocks  bow  in  a  quaquaversal  manner,  in- 
dicating that  many  of  the  diabases,  gabbros,  and  diorites  are  intrusive 
subsequent  to  the  formation  of  the  Marquette  series,  and  that  the 
local  strikes  and  dips  are  often  due  to  this  cause. 
Van  Hise,51  in  1890,  examined  the  rock  succession  at  Iron  Moun- 
tain, Michigan.  Overlying  the  ore  formation  of  the  Ludington  and 
Chapin  mines  is  a  conglomerate  which  bears  fragments  of  ore  and 
jasper.  It  therefore  appears  that  after  this  material  reached  its  pres- 
ent condition  in  the  ore-bearing  series  it  was  eroded  and  furnished 
debris  for  a  newer  series. 
Williams,52  in  1890,  as  a  result  of  an  extended  examination  of  the 
field  relations  and  microscopical  characters  of  the  widespread  green- 
stones, greenstone  schists,  and  agglomerates  of  the  Marquette  and 
Menominee  districts,  concludes  that  they  are  all  of  eruptive  origin. 
This  conclusion  is  reached  from  a  consideration  of  the  field  evidence, 
the  schistose  phases  being  frequently  traced  by  continuous  gradations 
into  massive  forms,  and  of  the  microscopical  evidence,  these  unal- 
tered forms  having  all  the  characteristics  of  eruptive  rocks.  The 
original  rock  types  were  rather  numerous,  including  gabbro,  diabase, 
diabase  porphyry,  melaphyre,  diorite,  diorite  porphyry,  and  tuffs. 
These  rocks  have  been  compressed,  faulted,  and  crushed,  as  a  result  of 
