AREA   NORTH   AND    NORTHEAST   OF   LAKE    HURON.  431 
enable  a  boundary  to  be  placed  between  them.  Together  they  prob- 
ably constitute  the  exposed  edges  of  a  laccolith  folded  into  a  basin 
shape  and  containing  in  its  depressed  interior  the  Upper  Huro- 
nian  (?),  as  held  by  Coleman.  The  nickel  is  mainly  in  the  form 
of  a  nickel-iron  sulphide,  pentlandite,  associated  with  pyrrhotite  and 
chalcopyrite.  It  is  believed  to  be  essentially  an  original  constituent 
of  the  norite  magma,  although  locally  segregated  through  the  agency 
of  hot  gaseous  and  aqueous  solutions  accompanying  later  stages  of 
the  norite  eruption. 
Kay,59  in  1904,  describes  the  rocks  seen  on  a  trip  from  Mattagami 
to  Nighthawk  and  the  area  west  of  Lake  Abitibi.  No  attempt  is 
made  to  describe  their  stratigraphy  and  structure. 
Miller,00  in  1904  and  1905,  maps  and  describes  the  silver-cobalt 
area  near  Haileybury,  on  the  northwest  shore  of  Lake  Temiskaming, 
Ontario.     The  succession  is  as  follows,  from  the  base  up : 
1.  Laurentian.     Lorrain  granite.     This  granite  is  intrusive  into  the  Keewatin, 
hut  not  into  the  Lower  Huronian. 
Igneous  contact. 
2.  Keewatin.     This   series    is   an    igneous   complex,   consisting   of   greenstones, 
quartz  porphyries,  and  other  rocks.     It  has  been  more  or  less  folded  and 
disturbed. 
Great  unconformity. 
o.  Lower  Huronian.  The  Cobalt  series,  consisting  of  conglomerate,  breccia, 
quartzites,  and  graywacke  slate.  Outcrops  of  the  coarser  varieties  of  the 
rocks  are  confined  almost  entirely  to  the  area  east  of  a  line  which  rims 
from  the  east  side  of  Mud  Lake  northeastward  to  about  lot  6  in  the  fifth 
concession  of  Bucke.  West  and  southwest  of  this  line  there  is  much  red- 
dish banded  slate  and  quartzose  graywacke.  The  cobalt-nickel-arsenic- 
silver  veins  occur  largely  in  this  series. 
Unconformity. 
4.  Middle  Huronian.     Lorrain  arkose,  quartzite,  and  conglomerate. 
5.  Diabase  and  gabbro.     These  igneous  rocks  cut  through  all  the  other  pre-Cam- 
brian  series  in  the  field.     Their  exact  age  is  not  known.     They  may  belong 
either  to  Animikie  or  Keweenawan  time.     The  ores  of  the  district  may 
have  been  deposited  from  highly  heated  mineral-laden  waters  associated 
with  the  eruption. 
Great  unconformity. 
6.  Niagara.     Limestone  with  a  small  amount  of  sandstone  and  conglomerate  at 
its  base. 
Tngall  and  Denis,01  in  1905,  report  on  the  geology  of  the  country 
around  the  Bruce  mines.  Corrections  are  made  in  tin1  area!  distribu- 
tion of  the  part  of  Logan  and  Murray's  Original  Huronian  succession 
found  in  this  area. 
Parks,62  in  1905,  reports  on  (lie  geology  of  a  district  from  Lake 
Temiskaming  northward,  including  a  part  of  the  Cobalt  district. 
The  description  of  the  Cobalt  district  is  similar  to  that  given  by  Mil- 
ler, though  the  classification  and  nomenclature  used  by  Miller  are  not 
followed.  In  the  country  to  the  north  rocks  of  a  similar  nature  ox- 
tend  in  a  somewhat  narrow  band  from  the  outlet  of  Windiffo  Lake. 
