268  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
diabase,  and  there  is  a  strong  interaction  between  the  sedimentary 
and  eruptive  rocks. 
McKellar,249  in  1888,  describes  the  Animikie  on  the  north  shore  of 
Lake  Superior  as  always  resting  unconformably  upon  the  crystalline 
and  schistose  rocks  to  which  the  term  Huronian  is  applied,  the  con- 
tacts being  found  at  many  points.  In  lithological  characteristics 
these  two  series  are  fundamentally  different.  The  original  Huronian 
and  the  schists  underlying  the  Animikie  are  compared,  and  it  is  con- 
cluded that  they  are  the  equivalent  of  these  rocks  rather  than  of  the 
Animikie  series;  therefore  the  latter  is  later  than  the  Huronian. 
The  contacts  of  the  Animikie  and  Keweenawan  formations  show  that 
there  is  an  unconformity  by  erosion  between  the  two. 
Lawson,250  in  1888,  reports  on  the  geology  of  the  Rainy  Lake 
region.  The  pre-Cambrian  rocks  are  divided  into  an  upper  and  a 
lower  Archean,  as  at  the  Lake  of  the  Woods.  The  upper  is  a  bedded 
schistose  and  metamorphic  series,  while  the  lower  is  granitic,  gneissic, 
or  syenitic  in  character.  In  the  upper  division  two  groups  are  recog- 
nized, one  the  Keewatin  of  the  Lake  of  the  Woods,  and  the  other, 
inferior  in  position,  is  given  the  name  Coutchiching.  In  the  lower 
division  distinctions  of  stratigraphical  sequence  and  relationship,  if 
any  such  ever  existed,  have  been  obliterated,  and  for  this  the  term 
Laurentian  is  retained.  These  rocks  can  be  classified  only  on  a  petro- 
graphical  basis.  The  contacts  of  the  Keewatin  with  the  Coutchich- 
ing and  Laurentian  are  very  numerous.  The  relations  between  the 
Keewatin  and  Laurentian  are  exactly  like  those  described  as  existing 
at  the  Lake  of  the  Woods.  The  schists  are  intruded  by  the  granite, 
fragments  of  the  former  being  included  in  the  latter,  and  they  are 
sometimes  fused  at  the  contact.  Very  frequently  near  the  point  of 
junction  the  Keewatin  rocks  become  more  crystalline  and  are  glisten- 
ing hornblende  schists. 
At  two  localities  basal  conglomerates  are  found  between  the  Keewa- 
tin  and  Coutchiching.  At  the  first  of  these,  Ratroot  Bay,  Keewatin 
conglomerate  rests  upon  Coutchiching  schists,  the  conglomerates  con- 
taining waterworn  fragments  of  quartz  and  bowlders  of  granite. 
The  second  is  at  Grassy  Lake,  where  there  is  a  pebbly  conglomerate 
at  the  base  of  the  Keewatin.  The  contacts  of  the  Keewatin  and 
Coutchiching  are  usually  in  apparent  conformity,  and  the  mapping 
of  the  series  is  made  to  rest  upon  lithological  characters  rather  than 
upon  structural  discordance,  although  it  is  recognized  that  the  con- 
glomerates at  the  two  localities  mentioned  are  indicative  of  erosion, 
at  least  in  some  places,  between  the  two  series.  The  apparent  accord- 
ance affords  little  evidence  as  to  the  question  of  original  conformity 
or  unconformity,  because  the  two  formations  have  been  squeezed  to- 
gether; but  the  marked  contrast  in  lithological  characters  indicates 
an  abrupt  change  in  the  conditions  of  formation. 
