AREA   NORTH   AND   NORTHEAST   OF   LAKE    HURON.  441 
GENERAL    CORRELATION    AND    NOMENCLATURE    OF    HURONIAN    SERIES. 
The  two  sedimentary  groups  of  the  original  Huron ian  district — 
that  is,  the  portion  of  the  north  shore  of  Lake  Huron  mapped  in 
detail  by  Logan  and  Murray — have  been  called  the  upper  and  lower 
Huronian  series  by  Irving,  Van  Hise,  Pumpelly,  and  their  associates, 
and  the  upper  of  the  two  groups  has  been  correlated  with  the  Anim- 
ikie  group.  On  the  other  hand,  the  Canadian  geologists  have  uni- 
formly held  that  the  Animikie  is  younger  than  the  original  Huronian 
series  and  that,  for  this  reason,  it  should  not  be  called  Huronian.  The 
retention  of  the  Animikie  in  the  Huronian,  notwithstanding  the 
recognition  of  the  fact  that  the  Animikie  is  younger  than  the  series 
of  the  original  Huronian  district  proper,  is  believed  to  be  warranted 
by  the  following  facts:  Logan  and  Murray  in  1863  applied  the  term 
"  Huronian  "  to  what  they  believed  to  be  essentially  a  sedimentary 
series  on  the  north  shore  of  Lake  Huron.  Where  it  was  mapped  in 
detail  (1863)  by  Logan  and  Murray  it  has  been  subsequently  found 
to  include  two  sedimentary  groups  resting  on  an  igneous  basement. 
But  at  the  same  time  they  published  a  general  map  showing  the  dis- 
tribution of  the  "  Huronian  "  for  the  region  as  a  whole,  and  on  that 
map  both  the  Animikie  of  the  north  shore  of  Lake  Superior  and  the 
sediments  to  the  northwest  of  Sudbury,  later  mapped  by  Bell  as 
"  Cambrian,"  are  included  under  the  "  Huronian."  While  both  are 
now  recognized  as  overlying  the  Huronian  series  of  the  original 
Huronian  district  proper,  it  is  believed  that  both  are  entitled  to  the 
term  Huronian.  A  threefold  division  takes  the  place  of  a  twofold 
division  of  this  series.  Logan  and  Murray  did  not  subdivide  the 
series  at  all,  and  hence  the  twofold  division  previously  held  for  the 
region  as  a  whole  does  not  have  the  authority  of  their  mapping  any 
more  than  the  threefold  division  now  proposed. 
The  joint  geological  committee  in  1901  adopted  the  threefold  divi- 
sion of  the  Huronian,  and  is  thus  in  essential  accord  with  the  above 
conclusions.    The  committee  did  not  cover  all  of  the  district. 
There  are,  then,  two  unconformable  sedimentary  groups  in  the  orig- 
inal Huronian  district  proper.  Logan's  general  map  of  the  Huronian 
included  the  Sudbury  region  to  the  northeast,  where  there  is  a  sedi- 
mentary group  (Bell's  Cambrian,  Barlow's  and  Coleman's  Upper 
Huronian)  which  is  younger  than  either  of  the  two  groups  of  the* 
original  Huronian  district.  The  Huronian  series  of  the  general 
region  north  of  Lake  Huron  is  therefore  divided  into  three  groups — 
upper  Huronian,  lower  Huronian,  and  middle  Huronian.  The  upper 
Huronian  is  similar  in  lack  of  folding  and  metamorphism  and  in  part 
in  lithology  to  the  Animikie  group  of  the  north  shore  of  Lake 
Superior  and  is  correlated  with  that  group.  The  middle  and  lower 
Huronian  north  of  Lake  Huron  are  similar  in  lithology,  structure, 
