440  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
them  are,  in  different  areas,  one,  two,  or  possibly  three  unconformable 
groups,  cut  by  basic  and  acidic  intrusives,  assigned  to  the  Huronian. 
This  succession  and  nomenclature  appear  on  Miller's  map  of  the 
silver-cobalt  area  near  Haileybury,  on  Lake  Temiscaming,  and  on 
Brock's  map  of  the  Larder  Lake  district  to  the  north.  In  the  Cobalt 
district  the  Keewatin  is  identical  in  every  respect  to  that  of  the  Lake 
Superior  country,  and  particularly  to  that  of  the  Vermilion  district, 
Minnesota,  even  to  the  existence  of  ellipsoidal  structures  in  the  basalt 
and  intrusion  by  peculiar  "  white-eyed  "  quartz  porphyries.  Lau- 
rentian  granites  and  gneisses  intrude  the  Keewatin.  Resting  upon 
both,  with  marked  unconformity,  are  two  Huronian  groups  of  slates 
and  quartzites,  correlated  with  the  middle  and  lower  Huronian.  The 
upper  group  is  much  less  metamorphosed  than  the  lower.  The  cor- 
relation with  the  middle  and  lower  Huronian  rather  than  with  the 
upper  and  middle  or  the  upper  and  lower  is  tentative  and  not  sup- 
ported by  structural  evidence.  Intrusive  into  all  the  groups  are 
gabbro  and  diorite,  provisionally  correlated  with  the  Keweenawan. 
Miller  believes  that  a  similar  succession  exists  somewhat  widely 
beyond  the  limits  of  his  map  in  all  directions.  Van  Hise  and  Leith 
have  mapped  about  a  thousand  square  miles  in  the  area  extending 
from  Lake  Temagami  westward  to  Lake  Onaping  and  in  the  area 
northward  from  Biseotasing,  and  find  similar  groups  with  similar 
relations  throughout  these  areas,  but  whether  two  or  three  Huronian 
groups  are  present  is  not  yet  known. 
Brock  has  found  the  same  groups  and  relations  in  the  Larder 
Lake  district  of  the  Height  of  Land  north  of  Lake  Temiscaming. 
The  relations  of  the  granites  and  gneisses  to  the  sedimentary  rocks 
of  this  region  have  been  disputed.  The  Temagami  area  has  been 
cited  by  Barlow  as  affording  strong  evidence  of  the  intrusion  of  the 
Laurentian  granites  into  the  Huronian  sediments.  An  examination 
of  the  contact  at  two  places  by  Van  Hise  and  Leith  in  1903  showed 
conclusively  that  the  Huronian  series  rests,  with  normal  erosion  un- 
conformity with  clearly  defined  conglomerates,  against  the  Lauren- 
tian granites.  These  conglomerates  had  previously  been  referred  to  as 
breccias.  Miller's  map  of  the  Cobalt  area  to  the  north  shows  similar 
facts.  The  existence  of  conglomerates  and  the  fact  that  granite  is 
unconformably  below  the  Huronian  series  are  now  admitted  by  Bar- 
low, but  he  still  is  inclined  to  hold  that  much  the  larger  part  of  the 
granite  is  intrusive  into  the  Huronian  series.  We  are  not  prepared  to 
state  what  part  of  the  granite  is  unconformably  below  the  Huronian 
series,  but  our  mapping  in  this  area,  extending  over  1,000  square 
miles,  has  shown  the  presence  of  a  much  larger  amount  of  pre-Huro- 
nian  than  Huronian  or  post-Huronian  granite. 
