LAKE    SUPERIOR   REGION.  281 
neighborhood  of  Rat  Portage,  and  the  vicinity  of  Fort  William  on 
Lake  Superior.  As  in  previous  reports,  the  general  geology  worked 
but  by  Lawson  for  the  Lake  of  the  Woods  and  Rainy  Lake  districts  is 
accepted,  and  the  general  principles  are  applied  to  other  districts  of 
the  region  visited. 
In  previous  years  it  has  been  held  that  gold  was  to  be  looked  for 
only  in  the  Huronian.  During  the  last  three  years,  however,  it  has 
been  found  that  some  of  the  most  promising  gold  deposits  occur  in 
the  granite  or  the  gneiss.  It  has  also  been  found  that  the  best  veins 
or  other  ore  deposits  occur  at  or  near  the  contact  of  the  Laurentian 
eruptive  rocks  and  the  Huronian. 
In  the  Ontario  region  the  gold  deposits  occur  in  the  following 
ways:  (1)  True  fissure  veins,  commonly  found  in  the  areas  of  mas- 
sive eruptive  granite.  (2)  Lenticular  or  bedded  veins,  confined  to  the 
schistose  rocks.  These  are  intercalated  between  the  schists  and  run 
parallel  with  their  strike,  and  are  not  so  continuous  as  the  fissure 
veins.  (3)  Contact  deposits,  between  the  Huronian  and  the  Lauren- 
tian. These  are  rare  in  this  district.  (4)  Fahlbands  of  schists,  im- 
pregnated with  pyrites  and  other  sulphides.  (5)  In  quartz,  asso- 
ciated with  dikes  of  porphyry  or  felsite,  near  the  contact  of  the  Hu- 
ronian and  Laurentian  rocks,  penetrating  the  schists,  and  sometimes 
the  granite  itself.  (6)  In  an  eruptive  mass,  in  but  one  locality.  (7) 
Placer  deposits. 
Willmott,269  in  1898,  describes  the  geology  of  the  Michipicoten 
mining  division,  which  is  limited  on  its  eastern  side  by  the  84th  merid- 
ian, on  the  west  by  Lake  Superior,  on  the  south  by  latitude  47°  30',  and 
on  the  north  by  latitude  48°  30'.  Most  of  the  rocks  of  the  area  belong 
to  the  Laurentian  and  Huronian.  The  northern,  eastern,  and  south- 
eastern portions  of  the  area  are  occupied  by  the  Laurentian ;  the  cen- 
tral and  southwestern  portions  by  the  Huronian.  The  Laurentian 
is  almost  everywhere  a  fine-grained  gray  gneiss,  which  often  becomes 
granitic  and  coarser  grained  in  texture.  The  Huronian  rocks  are 
most  commonly  massive  diorites  and  diabases  and  hornblende  and 
chlorite  schists;  less  commonly  they  are  slates,  felsites,  quartzites,  and 
sericite  slates.  The  Laurentian  is  frequently  in  eruptive  contact  with 
the  Huronian. 
In  two  areas  the  Nipigon  or  Keweenawan  rocks  overlie  the  Huro- 
nian and  Laurentian  rocks.  One  of  these  areas  is  2  miles  north 
of  Cape  Choyye,  and  the  other  is  on  the  peninsula  of  Gargantua. 
Parks,270  in  1898,  describes  the  geology  of  the  base  and  meridian 
lines  in  the  Rainy  River  district,  in  an  area  extending  from  Lac  Seul 
on  the  northwest  and  Lake  Wabigoon  on  the  southwest'  to  Sturgeon 
Lake  and  Mattawa  Lake  on  the  east.  Laurentian  and  Huronian  rocks 
occur  in  folds  with  a  general  noil heast -southwest  trend.  The  Huro- 
nian rocks  occur  in  three  main  areas — the  Sturgeon   River  area,  the 
