vanhisb.1  LAKE    SUPERIOE    REGION.  153 
Above  the  Penokee  .series  are  the  Keweenawan  rocks,  which  are  found 
at  Tyler's  fork  above  a  thickness  of  at  least  13,000  feet  of  sediments 
belonging  to  the  Penokee  series.  In  passing  east  or  west  from  this 
point  the  Keweenawan  rocks  come  in  contact  with  lower  and  lower 
horizons  of  the  Penokee  series.  At  one  place  the  entire  succession 
appears  to  be  cut  off  by  it.  This  is  taken  to  imply  that  between  the 
deposition  of  the  Penokee  series  and  the  outflows  of- Keweenawan  time 
there  lapsed  a  sufficient  time  for  erosion  to  remove  at  least  this  thick- 
ness of  sediments,  and  consequently  that  between  the  Keweenawan 
and  Penokee  series  is  a  very  considerable  unconformity. 
This  unconformity  is  not,  however,  evident  in  single  cross-sec- 
tions. The  bedded  Keweenawan  traps  have  a  high  inclination  which 
is  not  markedly  different  from  that  of  the  Penokee  succession.  The 
inclination  of  this  bedding  is  ascertained  by  the  contacts  of  the  differ- 
ent flows,  by  the  inclination  of  their  amygdaioidal  horizons,  and,  north 
of  Bessemer,  by  the  contact  between  the  traps  and  an  interleaved  sand- 
stone. 
At  lake  Gogebic  the  Eastern  sandstone  is  found  in  a  horizontal  posi- 
tion to  rest  against  the  upturned  edges  of  the  Southern  Complex  and 
Penokee  series  alike,  and  to  contain  numerous  characteristic  fragments 
which  can  have  been  derived  only  from  these  series.  Also  very  numer- 
ous fragments  are  found  equally  characteristic  of  the  Keweenaw  series, 
and  it  is  therefore  concluded  that  after  the  deposition  of  the  Penokee 
and  Keweenawan  series,  before  the  Eastern  sandstone  was  laid  down, 
that  the  two  former  were  upturned  and  suffered  great  denudation. 
A  comparison  of  the  Penokee  series  proper  and  the  Animikie  series 
shows  that  they  are  made  up  of  like  succession  of  rocks,  occupying  the 
same  relative  positions  with  reference  to  overlying  and  underlying  rocks, 
one  dipping  northward  under  the  basin  of  lake  Superior  and  the  other 
dipping  southward  under  the  same  body  of  water.  They  are  therefore 
regarded  as  equivalent.  As  probably  equivalent  with  the  Penokee 
series  are  also  placed  the  various  areas  of  rocks  in  the  lake  Superior 
basin  referred  to  the  Upper  Huronian. 
A  comparison  of  the  Penokee  with  the  Marquette  succession  shows 
that  there  is  a  very  close  correspondence.  Unconformably  below  the 
Marquette  and  Penokee  elastics  is  a  crystalline  basement  complex. 
Within  the  pre-Keweenawan  elastics  in  each  district  is  a  second  phys- 
ical break.  Below  this  break,  in  the  Penokee  district,  the  formations 
tof  the  lower  Marquette  are  now  represented  only  by  the  Oherty  Lime- 
stone. That  other  members  once  existed  is  indicated  by  the  presence  of 
fragments  of  jasper  and  quartzite  in  the  lowest  horizon  of  the  Quartz- 
Slate.  Formations  conqwsed  of  these  rocks  and  a  cherty  limestone 
are  the  characteristic  members  of  the  lower  Marquette. 
The  correspondence  of  the  members  of  the  Penokee  series  proper 
with  those  of  the  upper  Marquette  is  complete.  The  upper  Marquette 
and  Penokee  series,  looked  at  broadly,  are  great  slate  formations,  both 
