294  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
Van  Hise,  Bell,  Adams,  Miller,  Hayes,  Seaman,  and  Leith,8s 
in  1904,  visited  the  Rainy  Lake  district.  At  the  east  end  of  Shoal 
Lake  the  Coutchiching  schists  form  the  highest  formation.  These  are 
a  series  of  micaceous  schists  graduating  downward  into  green  horn- 
blendic  and  chloritic  schists,  here  mapped  by  Lawson  as  Keewatin, 
which  pass  into  a  conglomerate  known  as  the  Shoal  Lake  conglom- 
erate. This  conglomerate  lies  upon  an  area  of  green  schists  and 
granites  known  as  the  Bad  Vermilion  granites.  It  holds  numerous 
large,  well-rolled  fragments  of  the  underlying  rocks  and*  forms  the 
base  of  the  sedimentary  series.  It  is  certain  that  in  this  line  of  sec- 
tion the  Coutchiching  is  stratigraphically  higher  than  the  chloritic 
schists  and  conglomerates  mapped  as  Keewatin.  On  the  south  side 
of  Rat  Root  Bay  there  is  also  a  great  conglomerate  belt,  the  dominant 
fragments  of  which  consist  of  green  schist  and  greenstone,  but  which 
also  contain  much  granite. 
In  the  Lake  of  the  Woods  area  the  party  (except  Hayes)  made  one 
main  section  from  Falcon  Island  to  Rat  Portage,  with  various  trav- 
erses to  the  east  and  west  of  the  line  of  section.  The  section  was  not 
altogether  continuous,  but  a  number  of  representatives  of  each  for- 
mation mapped  by  Lawson  were  visited.  Lawson's  descriptions 
were  found  to  be  substantially  correct.  Belts  of  sedimentary  slate 
of  any  considerable  magnitude  were  not  found.  At  one  or  two  local- 
ities subordinate  belts  of  slate  which  appeared  to  be  ordinary  sedi- 
ment, and  one  narrow  belt  of  black  slate  which  is  certainly  sediment, 
were  found.  Many  of  the  slaty  phases  of  rocks  seemed  to  be  no  more 
than  the  metamorphosed  ellipsoidal  greenstones  and  tuffs,  but  some 
of  them  may  be  felsite.  However,  it  is  not  asserted  that  larger  areas 
may  not  be  sedimentary  in  the  sense  of  being  deposited  under  water. 
Aside  from  the  belts  mapped  as  slate,  there  are  great  areas  of  what 
Lawson  calls  agglomerate.  These  belts  mapped  as  agglomerates 
seem  to  us  to  be  largely  tuff  deposits,  but  also  include  extensive  areas 
of  ellipsoidal  greenstone.  At  a  number  of  places,  associated  and 
interstratified  with  the  slaty  phases,  are  narrow  bands  of  ferruginous 
and  siliceous  dolomite.  For  the  most  part  the  bands  are,  less  than  a 
foot  in  thickness,  and  no  band  was  seen  as  wide  as  3  feet,  but  the 
aggregate  thickness  of  a  number  of  bands  at  one  locality  would 
amount  to  several  feet. 
No  structural  breaks  between  the  above-mentioned  formations  of 
the  Lake  of  the  Woods  could  be  discovered.  The  various  classes  of 
materials — slates,  agglomerate,  and  ellipsoidal  greenstones — all 
seem  to  belong  together.  In  short,  these  rocks  on  the  Lake  of  the 
Woods  seem  to  constitute  one  series  which  is  very  largely  igneous  or 
volcanic  in  origin,  but  does,  as  above  mentioned,  contain  sediments. 
This  series  in  the  Lake  of  the  Woods  area  is  the  one  for  which  the 
term  Keewatin  was  first  proposed  for  the  greenstone  series,  Lawson 
