LAKE    SUPERIOR   REGION.  265 
The  Laurentian  are  essentially  granitoid,  gneissic,  and  feldspathic, 
while  the  Huronian  are  quartzose,  hornblendic,  schistose,  and  slaty. 
As  a  whole  the  latter  have  a  somewhat  altered  aspect  and  contain 
pebbles  of  rocks — granite,  gneiss,  qnartzite,  etc. — similar  to  those 
which  form  the  Laurentian  strata  beneath  them,  while  others,  how- 
ever, are  not  recognizable  as  from  any  known  Laurentian  sources. 
Bands  of  limestone  and  dolomite,  more  or  less  crystalline,  are  found 
in  both  Laurentian  and  Huronian  areas,  and,  if  we  except  the  dis- 
puted form  Eozoon,  no  fossil  whatever.  The  Huronian  follows  and 
does  not  rest  unconformably  upon  the  Laurentian.  The  Nipigon 
or  Keweenian  is  later  in  age  than  the  Animikie.  No  definite  opinion 
can  be  expressed  as  to  the  position  of  the  crowning  overflow  of 
Thunder  Cape. 
Selwyn,245  in  1883,  describes  the  trap  and  sandstone  of  Lake  Supe- 
rior as  unconformably  upon  and  entirely  distinct  from  the  Huronian. 
The  series  is  divisible  on  the  Canadian  shore  into  two,  and  perhaps 
three,  divisions,  between  which  there  may  be  slight  unconformities, 
which  are,  however,  no  greater  than  might  be  occasioned  by  the  inter- 
mingling of  sedimentary  strata  with  volcanic  material.  The  groups 
are,  in  ascending  order :  ( 1 )  The  shales,  cherts,  dolomites,  and  sand- 
stones, interbeclded  with  massive  diabase  or  dolerite,  of  Pie  Island, 
McKays  Mountain,  and  Thunder  Cape,  (2)  Conglomerates,  shales, 
sandstones,  and  dolomites,  interstratified  with  massive  beds  of  vol- 
canic material,  amygdaloids,  melaphyres,  tuffs,  etc.,  many  thousands 
of  feet  thick,  occupying  the  east  shore  of  Black  Bay,  Nipigon  Strait, 
St.  Ignace,  Michipicoten  Island,  Gargantua,  Mamainse,  etc.  (3) 
The  Sault  Ste.  Marie  sandstone,  which  may  be  only  the  upper  part  of 
2  without  any  intermingling  of  volcanic  material.  The  whole  to- 
gether is  lower  Cambrian,  there  being  no  evidence  whatever  of  their 
holding  any  other  place  in  the  geological  series.  The  first  of  these 
groups  is  the  Animikie  series,  while  the  second  is  the  Keweenian. 
Selwyn,-4'1  in  1885,  places  the  crowning  overflow  of  McKays 
Mountain,  Thunder  Cape,  and  Pie  Island,  etc.,  as  a  part  of  the  Anim- 
ikie. There  was  found  no  evidence  of  unconformity  from  the  base 
of  the  Animikie  to  the  top  of  the  Keweenian  as  developed  on  Thun- 
der Cape  and  in  the  surrounding  region. 
Lawson,247  in  1886,  gives  a  report  on  the  geology  of  the  Lake  of  the 
Woods  region,  with  special  reference  to  the  Keewatin  (Huronian?) 
belt  of  the  Archean  rocks. 
Comprising  a  large  part  of  the  Lake  of  the  Woods  is  a  series  of 
crystalline  and  semicrystalline  schists  to  which  the  term  Keewatin 
is  applied.  The  term  Huronian  is  not  used,  because  it  is  very  doubt- 
ful if  the  series  belongs  to  this  period.  The  rocks  are  found  to  dif- 
fer fundamentally  in  lithological  character  from  Logan's  Original 
Huronian. 
