vanhise.]  LAKE    SUPERIOR    REGION.  171 
per  only  if  the  schists  are  of  sedimentary  origin.  The  investigations 
of  Irving,  Williams,  and  the  Profs.  Winchell,  as  well  as  our  own  later 
work,  have  shown  that  the  lower  Vermilion  and  lower  Marquette  iron- 
bearing  members  contain  many  schistose  dikes,  and  also  that  in  many 
cases  the  massive  greenstone  knobs  found  in  these  districts  vary  by 
imperceptible  stages  into  the  finely  laminated  schists  associated  with 
the  irou  ore  and  jasper.  The  schists  are,  then,  in  part  at  least,  of  erup- 
tive origin.  Brooks  noted  the  dike-like  character  of  certain  magnesian 
schists  associated  with  the  ore  formation,  between  which  and  the  dio- 
ritic  schists,  believed  to  be  of  sedimentary  origin,  it  was  said  to  be 
impossible  to  draw  the  line.  That  these  well  laminated  schists  should 
not  at  first  be  regarded  as  eruptive  is  natural,  but  the  variation  of 
massive  igneous  rocks  into  those  which  are  well  laminated  as  a  result 
of  dynamic  action  and  metasomatic  changes  is  now  so  Avell  known  that 
new  cases  of  it  excite  no  surprise.  I  would  by  no  means  assert  that 
all  of  the  schistose  rocks  associated  with  the  iron  ores  and  jaspers  in 
the  Marquette  and  Vermilion  districts  are  of  eruptive  origin,  but  this 
is  certainly  the  case  at  many  localities.  This  view  reverses  Wads- 
worth's  and  makes  his  sedimentary  rocks  eruptive  and  his  eruptives 
sedimentary.  It  will,  however,  be  seen  that  this  position  harmonizes 
Irving's  conclusion  as  to  the  sedimentary  origin  of  the  ores  and  jaspers 
and  the  point  upon  which  Wads  worth  places  most  emphasis,  that  there 
are  eruptive  contacts  between  these  rocks  and  the  associated  schists. 
It  is  to  be  noted  that  the  eruptive  theory  has  been  applied  only  to  the 
Marquette  and  Vermilion  jasper  and  ore.  No  one  has  asserted  such  an 
origin  for  the  iron-bearing  horizon  of  the  Penokee  and  Animikie  series. 
This  is  an  independent  question,  as  will  be  seen  by  what  follows;  for 
these  formations  probably  occupy  a  higher  position  than  the  lower  Mar- 
quette and  lower  Vermilion  ores.  We  have,  then,  to  answer  two  ques- 
tions: "What  is  the  origin  of  the  iron -ore  formations  of  the  Penokee, 
Animikie,  and  equivalent  iron-bearing  formations?"  and,  second,  "What 
is  the  origin  of  the  great  masses  of  ore  and  jasper  of  somewhat  irregu- 
lar shape,  apparently  not  continuous  formations,  although  probably  at 
rather  persistent  horizons,  in  the  Lower  Vermilion,  Lower  Marquette, 
Kaministiquia,  and  similar  areas!" 
Upon  the  first  of  these  questions  there  is  practically  no  dispute.  The 
iron-ore  formation  in  the  Penokee  district  has  been  found  to  extend  for 
many  miles  as  a  simple  belt  of  very  uniform  thickness  between  two  read- 
ily recognized  detrital  formations,  all  with  a  common  strike  and  dip 
varying  within  very  narrow  limits.  A  precisely  similar  condition  of 
affairs  is  found  in  the  Animikie  district.  These  formations  have  been 
shown  by  later  work  to  have  been  originally  altogether  what  they  still 
are  largely,  thinly  laminated  impure  cherty  carbonates  of  iron,  in  every 
way  analogous  to  similar  earthy  carbonates  of  later  geological  periods 
The  other  forms  of  material  now  associated  with  them,  such  as  jasper, 
actinolitic  and  maguetitic  schists,  ore  bodies,  etc.,  are  the  consequence 
