LAKE    SUPERIOR   REGION.  143 
fragments,  with  their  greater  length  parallel  to  the  schistose  struc- 
ture, are  found  with  their  longer  diameters  in  the  direction  of  the 
bedding  of  the  slate,  showing  that  their  schistosity  was  produced  be- 
fore the}^  were  broken  from  their  original  position.  It  is  then  con- 
cluded that  the  Southern  Complex  is  separated  from  the  Penokee 
series  by  a  great  unconformity,  and  that,  as  the  quartz  slate  is  per- 
sistent for  a  distance  of  many  miles,  the  underlying  complex  had 
nearly  reached  a  base-level  before  the  overlying  series  was  deposited. 
Above  the  Penokee  series  are  the  KeweenaAvan  rocks,  which  at 
Tylers  Fork  are  found  above  a  thickness  of  at  least  13,000  feet  of  sed- 
iments 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  suc- 
cession appears  to  be  cut  off  by  it.  This  is  taken  to  imply  that  be- 
tween the  deposition  of  the  Penokee  series  and  the  outflows  of  Kewee- 
nawan time  a  sufficient  time  elapsed  for  erosion  to  remove  at  least  this 
thickness  of  sediments,  and  consequently  that  between  the  Keweena- 
wan and  the  Penokee  series  there  is  a  very  considerable  unconformity. 
This  unconformity  is  not,  however,  evident  in  single  cross  sections. 
The  bedded  Keweenawan  traps  have  a  high  inclination  which  is  not 
markedly  different  from  that  of  the  Penokee  succession.  The  incli- 
nation of  this  bedding  is  ascertained  by  the  contacts  of  the  different 
flows,  by  the  inclination  of  their  amygdaloidal  horizons,  and,  north 
of  Bessemer,  by  the  contact  between  the  traps  and  an  interleaved 
sandstone. 
At  Lake  Gogebic  the  Eastern  sandstone  is  found  to  rest,  in  a  hori- 
zontal position,  against  the  upturned  edges  of  the  Southern  Complex 
and  Penokee  series  alike,  and  to  contain  numerous  characteristic  frag- 
ments which  can  have  been  derived  only  from  these  series.  Also  very 
numerous  fragments  equally  characteristic  of  the  Keweenaw  scries 
are  found,  and  it  is  therefore  concluded  that  after  the  deposition  of 
the  Penokee  and  Keweenawan  series,  before  the  Eastern  sandstone 
was  laid  down,  the  two  former  were  upturned  and  suffered  great 
denudation. 
A  comparison  of  the  Penokee  series  proper  and  the  Animikie  scries 
shows  that  they  are  made  up  of  a  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 
