AREA   NORTH   AND   NORTHEAST   OF   LAKE    HURON.  427 
It  can  hardly  be  said  that  the  precise  age  of  any  of  these  groups  of 
rocks  is  known,  though  they  probably  range  from  the  base  of  the 
Upper  Huronian  to  the  Keweenawan,  including  the  Laurentian  as 
later  than  the  Upper  Huronian.  No  rocks  undoubtedly  of  Lower  Hu- 
ronian age  are  known  from  the  nickel  district  proper,  though  the 
ranges  of  banded  silica  and  magnetite  extending  through  Hutton  and 
Wisner  townships  to  the  north  of  the  nickel  area  evidently  belong  to 
the  Lower  Huronian.a  The  latter  rocks  occur,  so  far  as  known,  en- 
tirely inclosed  in  granites  and  gneisses,  generally  considered  Lauren- 
tian, and  have  not  been  found  in  direct  connection  with  the  rocks  here 
described. 
The  fact  has  been  brought  out  that  all  of  the  nickel  deposits  are 
either  on  the  basic  edge  of  a  great  eruptive  band,  which  at  the  oppo- 
site edge  becomes  a  quartz  syenite  or  granite,  or  on  dikelike  offshoots, 
often,  however,  interrupted  by  other  rocks  projecting  from  the  south- 
eastern basic  edge  of  the  great  gabbro  band.  This  band  has  been 
found  to  outcrop  in  a  great  oval,  the  north  and  south  sides  of  which 
have  been  known  respectively  as  the  North  and  South  nickel  ranges. 
The  structure  is  synclinal  and  the  center  is  occupied  by  Animikie  or 
Upper  Huronian  rocks. 
There  are  two  different  types  of  deposits  represented  in  the  mines 
of  the  district— those  along  the  southeastern  margin  of  the  main 
range,  often  crowded  into  baylike  indentations  of  the  adjoining  rock, 
and  those  strung  out  along  the  narrow  offshoots  from  the  main  range, 
as  Peters  suggests,  "  like  sausages  on  a  string,  but  with  a  long  piece 
of  string  between  the  sausages."  6  Among  the  former  class  are  the 
Creighton,  Gertrude,  Elsie,  Murray,  and  Blezard  mines;  among  the 
latter,  the  Copper  Cliff,  Evans,  Frood  and  Stobie,  and  the  Victoria 
and  Worthington  mines.  Perhaps  a  third  variety  should  be  distin- 
guished for  the  Vermilion  mine,  which  contains  rich  nickel  and  cop- 
per ores,  but  has  no  visible  association  with  a  band  of  gabbro,  having, 
however,  been  formed  probably  by  hot  circulating  fluids  proceeding 
from  such  a  band. 
The  final  impression  left  is  that  the  marginal  type  of  deposit  is  in 
the  main  of  plutonic  origin,  aqueous  work  having  been  relatively  un- 
important;  that  in  the  offset  type  plutonic  is  generally  more  impor- 
tant than  aqueous  action,  though  one  example,  the  Worthington,  sug- 
gests more  complete  rearrangement  of  the  materials  by  circulating 
water,  thus  forming  a  transition  to  ordinary  vein  deposits  wholly  due 
to  water  action,  as  at  the  Vermilion  mine. 
Leith,50  in  1903,  describes  the  Moose  Mountain  iron  range  in  the 
township  of  Hutton  and  district  of  Nipissing.  Iron  formation  con- 
sisting of  magnetite,  of  banded  magnetite  and  quartz,  and  of  mag- 
aRept.   Bur.   Minos  Ontario,   1901,  p.   186. 
"Min.  Res.  Ontario,  p.  104. 
