LAKE    SUPERIOR   REGION.  279 
The  Laurentian  rocks  consist  chiefly  of  granite  gneisses  with  sub- 
ordinate quantities  of  granite  and  syenite.  The  Coutchiching  con- 
sists of  fine-grained  mica  schists  and  mica  gneisses,  which  show  rapid 
changes  in  composition  in  passing  from  one  layer  to  another,  thus 
suggesting  sedimentation.  These  rocks  are  usually  sharply  separated 
from  the  Laurentian,  but  at  Kice  Bay  the  writer  found  himself  in 
doubt  as  to  the  classification.  The  Coutchiching  series  is  regarded  as 
a  metamorphosed  sedimentary  one.  As  to  the  source  of  the  material 
there  is  no  very  definite  information,  unless  certain  gneisses  in  Sand 
Island  River  having  layers  differing  sharply  in  composition  be  looked 
upon  as  remnants  of  an  original  Laurentian  floor.  The  Keewatin 
is  a  series  of  eruptive  and  fragmental  rocks  of  great  thickness  and 
variety,  consisting  broadly  of  a  lower  division  of  basic  eruptives  and 
volcanic  ashes  and  of  an  upper  acidic  division.  The  bulk  of  the  lower, 
basic  portion  consists  of  diabases  with  some  gabbros  and  anorthosites, 
and  apparently  some  diorites.  Porphyroids  are  also  present.  The 
schistose  members,  often  interbedded  with  the  massive  altered 
eruptives,  near  the  contact  with  the  Laurentian  are  chiefly  hornblende 
schists,  but  in  other  localities  are  chlorite  schists.  Between  these  two 
are  numerous  transitions.  Graywackes  occur  at  several  localities,  and 
agglomerates  and  conglomerates  are  plentiful.  The  upper,  acidic 
division  includes  felsites,  sericite  schists,  and  quartz  porphyries. 
These  are  apparently  younger  than  the  green  schists  and  massive 
rocks  of  the  Keewatin,  but  the  two  divisions  are  conformable,  as  is 
also  the  whole  of  the  Keewatin  to  the  Coutchiching.  The  rocks  in- 
cluded in  the  Laurentian  are,  for  the  most  part  at  least,  intrusive  in 
the  Coutchiching  and  the  Keewatin.  In  the  Keewatin  are  various 
intrusive  granite  areas.  Cutting  all  of  the  previous  series  are  dike 
rocks,  which  may  be  regarded  as  consisting  of  an  acidic  division,  in- 
cluding granite,  and  pegmatite,  and  a  basic  division,  including  diabase 
and  quartz  diabase. 
Many  details  are  given  as  to  particular  occurrences  of  the  various 
rock  series.  The  occurrence  of  gold  in  Ontario  is  described,  and  inci- 
dentally the  rock  succession  in  the  Hastings  district  is  summarized. 
Gibson,203  in  1895,  gives  a  summary,  from  the  reports  of  the  Cana- 
dian Geological  Survey,  of  the  pre-Cambrian  geology  of  the  Hinter- 
land of  Ontario. 
Blue,264  in  1896,  sketches  the  geological  history  of  the  New  On- 
tario, which  includes  that  part  of  the  Province  of  Ontario  lying  be- 
yond Matawan  and  French  rivers  and  the  Nipissing,  Huron,  and  Su- 
perior lakes,  to  the  north  and  west  boundaries  of  the  province.  Lau- 
rentian and  Huronian  rocks  form  highlands  which  in  Archean  time 
were  the  most  important  physical  feature  of  North  America,  sweep- 
ing in  a  curve  through  what  is  known  in  our  time  as  the  regions  of 
Labrador,  Quebec,  Ontario,  and  the  Northwest  Territories.     While 
