leith.]  THE    LAKE    SUPERIOR    IRON    REGION    DURING    1903.  217 
essential  chemical  change  through  which  the  ores  have  been  developed 
from  the  cherty  iron  carbonate  is  oxidation  of  the  ferrous  iron  and 
carrying  away  of  silica  and  carbon  dioxide,  as  so  often  described  for 
other  parts  of  the  Lake  Superior  region. 
The  total  thickness  of  the  Vulcan  formation  is  about  650  feet,  of 
which  over  half  is  a  fragmental,  noniron-bearing  rock.  This  thick- 
ness is  small  as  compared  with  iron  formations  of  other  districts  of  the 
Lake  Superior  region. 
The  Hanbury  slate,  overlying  the  Vulcan  formation,  contains  iron- 
formation  material,  but  no  considerable  deposit  of  ore  has  thus  far 
been  discovered. 
MARQUETTE  DISTRICT. 
A  small  amount  of  field  work  in  the  Marquette  district  was  done  in 
1903  by  C.  K.  Leith  and  W.  N.  Smith,  with  a  view  to  determining  the 
extent  and  nature  of  an  unconformity  at  the  base  of  the  Ajibik 
quartzite  in  the  Lower  Huronian  series,  discovered  by  Prof.  E.  A. 
Seaman,  of  the  Michigan  School  of  Mines.  It  was  found  to  be  of 
considerable  importance  and  to  represent  a  time  interval  long  enough 
to  allow  of  truncation  by  erosion  of  the  underlying  series  to  a  very 
considerable  extent,  as  held  by  Professor  Seaman.  Evidence  of  the 
unconformity  was  found  at  a  number  of  places  along  the  north,  east, 
and  south  sides  of  the  Marquette  syncline.  As  a  result  of  this  work 
there  are  now  discriminated  three  distinct  unconformable- series  in  the 
so-called  Huronian  of  this  district.  The  important  bearing  of  this  on 
the  general  correlation  of  formations  in  the  Lake  Superior  and  Lake 
Huron  regions  is  obvious. 
The  Mesnard  quartzite  of  the  Lower  Huronian  series  was  carried  in 
the  mapping  some  distance  farther  west  than  on  the  previously  pub- 
lished maps  of  the  Marquette  district.  Toward  the  west  the  quartzite 
becomes  altered  to  a  sericite-  schist  and  is  discolored,  making  its  rec- 
ognition difficult  except  where  actually  followed  through  the  stages 
of  its  alterations.  The  western  portion  of  the  formation  had  been 
included  in  previous  mapping  with  the  Kitchi  schist  member  of  the 
Archean. 
The  Carp  River  fault  was  mapped  in  detail  and  found  to  have  a 
somewhat  different  attitude  and  larger  extent  than  previously  shown 
on  the  Marquette  maps. 
Important  changes  have  been  made  in  the  mapping  of  the  Palmer 
district,  principally  by  mining  companies  in  connection  with  their 
explorations  for  iron  ore  in  this  area.  Two  companies  have  prepared 
large-scale  detail  sheets  showing  not  only  all  the  surface  features  but 
many  underground  records.  One  of  the  most  conspicuous  changes 
is  the  introduction  of  one  and  perhaps  two  faults  to  explain  the 
distribution. 
