LAKE    SUPERIOR   REGION. 
Poplar  Lodge  and  Sturgeon  River,  and  tabulates  the  rocks  of  the 
region  as  follows: 
Later  eruptives — gabbro,  diabase,  etc. 
Lower  Huronian — conglomerate  and  probably  slate  and  arkose. 
Archean <  [Iron  formation. 
Keewatin J  Green  and  gray  scbists,  sometimes  sideritic. 
[Greenstones  and  volcanics. 
Many  details  of  distribution  are  given. 
Moore,297  in  1907,  reports  on  the  iron  ranges  around  Lake  Winde- 
gokan,  east  of  Lake  Nipigon,  Ontario.  The  rocks  of  the  district, 
classified  in  accordance  with  the  recommendations  of  the  international 
committee  on  pre-Cambrian  nomenclature  for  the  Lake  Superior 
region,  are  as  follows: 
Pleistocene — drift  and  swamp. 
Keweenawan — basic  eruptives. 
Lower  Huronian — coiiglomerate- 
*  Arkose. 
Iron  range. 
Carbonate  schists. 
Green  schists. 
Keewatin 
It  is  difficult  to  decide  whether  the  different  members  of  the 
Keewatin  series  are  arranged  in  their  proper  order  of  succession,  be- 
cause most  of  the  rocks  are  badly  decomposed  and  the  contacts  are 
so  poor  and  complicated  that  little  can  be  learned  from  them.  The 
Iron  range  fixes  a  definite  geological  horizon,  and  most  of  the  green 
schists  are  older  than  that  formation,  but  the  case  is  not  so  clear  with 
regard  to  the  position  occupied  by  the  carbonate  schists  and  arkoses. 
The  former  correspond  closely  in  composition  to  the  Wawa  tuffs  of 
the  Michipicoten  region,  and  we  have  placed  them  in  the  same  relative 
position  here. 
The  arkoses,  which  are  widely  distributed  in  the  region,  are  the 
most  troublesome  of  all  the  rocks  to  classify  in  their  proper  order. 
In  older  works  they  are  commonly  included  in  the  Upper  Huronian, 
and  on  account  of  the  presence  of  some  jasper  fragments  which  were 
seen  in  one  section  one  would  suppose  that  they  should  be  placed  in 
the  Huronian  above  the  conglomerate.  Another  thing  which  would 
make  it  appear  as  if  the  arkoses  were  later  than  the  conglomerate  is 
the  absence  in  many  places  of  any  sign  of  schistosity,  which  is  so  com- 
mon in  the  other  rocks.  But  in  some  parts  the  arkoses  are  rather 
schistose,  and  it  may  be  that  in  others  they  resisted  the  forces  which 
caused  the  schistosity  and  remained  massive,  just  as  portions  of  the 
greenstones  have  retained  their  original  structure  while  others  became 
schistose.  Also  the  absence  of  any  considerable  quantity  of  jasper,  or 
any  definite  relation  to  the  conglomerate,  which  would  fix  the  relative 
ages,  and  the  presence  in  the  region  of  arkoses  which  are  distinctly 
