vanhisb.]  LAKE    SUPERIOR    REGION.  179 
UNCONFORMITY   WITHIN   CLASTIC   SERIES. 
It  is  believed  that  many  of  the  further  difficulties  as  to  correlation  in 
the  districts  about  lake  Superior  have  arisen  from  the  failure  to  recog- 
nize a  third  physical  break  which  has  a  very  wide,  if  not  universal, 
extent  in  this  region.  The  early  Canadian  geologists  found  a  break  at 
the  base  of  the  Animikie,  and  while  this  series  was  first  placed  with 
the  Huronian,  the  fact  that  unconformably  below  it  was  another  series 
which  also  resembled  the  Huronian  led  the  later  Canadian  geologists 
to  exclude  the  entire  Animikie  from  the  Huronian,  and  they  have  thus 
restricted  the  term  in  this  district  to  the  pre- Animikie  Huronian  rocks. 
The  Michigan  and  Wisconsin  geologists  include  in  the  Huronian  the 
equivalents  of  both  the  Animikie  and  pre- Animikie  Huronian,  and  while 
facts  were  clearly  contained  in  their  reports  pointing  to  a  discordance 
within  the  rocks  referred  to  the  Huronian  no  attempt  was  made  to 
carry  these  facts  to  their  conclusion  and  to  subdivide  the  series.  But  as 
early  as  1883  Irving  saw  that  there  is  a  series  of  green  schists  and 
schist-conglomerates  which  must  rest  discordantly  below  other  rocks 
recognized  as  Huronian,  as  shown  by  their  attitude  and  degree  of  crys- 
tallization, as  well  as  by  the  fact  that  they  had  yielded  fragments  to 
the  newer  formations.  Asa  consequence  of  this  he  was  led  to  exclude 
from  the  Huronian  these  lower  schists,  which  had  before  been  every- 
where accepted  as  Huronian.  Lawson,  in  1886,  saw  that  his  Keewatin 
series  is  fundamentally  different  from  parts  of  the  original  Huronian, 
and  especially  from  the  Animikie  series,  and  was  led  to  refer  it  to  the 
Huronian  series  only  doubtfully  5  at  the  same  time  he  saw  that  the 
Keewatin  is  like  the  Dore  river  series  at  the  east  end  of  lake  Superior, 
and  suggested  that  possibly  Logan  and  Murray  had  placed  in  the 
Huronian  two  discordant  series.  Alexander  Winchell,  in  his  last 
paper,  which  appeared  almost  simultaneously  with  his  death,  announced 
definitely  that  two  series  had  beeu  confounded  in  the  Huronian. 
We  will  now  consider  the  evidence  for  a  physical  break  within  the 
rocks  which  have  generally  been  referred  to  the  Huronian. 
Evidence  of  this  break  in  the  Marquette  district  was  first  noticed  by 
Foster  and  by  Foster  and  Whitney,  who  found  over  the  ore  horizon  at 
what  has  since  become  the  Republic  mine,  and  one  or  two  other  locali- 
ties, a  conglomerate  bearing  fragments  of  the  ore,  jasper,  and  other  rocks 
associated  with  the  iron  ore.  It  was  next  noted  by  Kimball,  who 
mentions  beds  of  specular  conglomerate.  Credner  describes,  over  the 
iron  formation  at  Michigamme  mine,  a  conglomerate,  the  fragments 
of  jasper  and  quartz  being  in  an  iron  and  quartz  base.  Brooks 
(describes  the  upper  quartzite  of  Republic  mountain  and  that  at  the 
New  England  mine  as  a  conglomerate  containing  fragments  of  ore. 
By  Rominger  the  break  was  noticed  at  so  many  places  that  he  re- 
marked that  above  the  iron-bearing  rock  is  generally  a  very  coarse 
tyuartzite-conglomerate  which  often  has   the   character  of  a   coarse 
