AREA   NORTH   AND   NORTHEAST   OF   LAKE    HURON.  419 
crust  of  the  earth  has  caused  large  portions  of  the  Huronian  to  sink 
below  the  plane  of  fusion,  the  result  of  which  has  been  to  produce 
irruptive  contacts.  At  other  places,  as  described  by  Pumpelly  and 
Van  Hise,  the  Basement  Complex  may  have  remained  undisturbed, 
so  that  the  overlying  detritals  have  not  been  intruded  by  the  gran- 
itic mass  beneath. 
Barlow,35  in  1893,  describes  the  Laurentian  granites  and  gneisses 
as  intrusive  in  the  Huronian  rocks  north  of  Lake  Huron.  The  locali- 
ties described  are  Killarney  Village;  Beaver,  Fox,  Balsam,  Three 
Mile,  Brush,  Camp,  Crooked,  Johnny,  Panache,  Wavy,  Chief's,  Daisy, 
Baby,  and  Alice  lakes;  Goshen,  Broder,  and  Dell  townships;  Wah- 
napitae  River;  Cartier  and  Straight  Lake  stations;  and  two  islands 
near  Thessalon.  As  evidence  of  the  eruptive  nature  of  the  Lauren- 
tian gneiss  in  the  Huronian  sediments  are  cited  the  diverse  strati- 
graphic  relations  of  the  rocks  along  their  line  of  junction;  the  in- 
variable alteration  of  the  sedimentary  rocks  along  the  contact  line; 
the  inclusion  in  the  gneiss  of  angular  fragments  clearly  referable  to 
the  adjacent  sedimentary  strata;  the  occurrence  of  gneissic  intrusions 
and  apophyses  of  pegmatite  in  or  laminated  with  and  cutting  across 
the  bedding  of  the  Huronian  rocks ;  the  absence  of  sedimentary  rocks 
within  the  gneiss,  and  the  general  character  of  the  gneiss,  which,  in 
appearance  and  behavior,  more  nearly  resembles  an  eruptive  granite 
than  an  altered  sedimentary  rock.  It  is  therefore  concluded  that 
the  Huronian  is  the  oldest  series  of  sedimentary  strata  in  this  region, 
and  that  the  floor  upon  which  these  were  laid  down  must  have  been 
subsequently  fused  and  recrystallized. 
Bell,36  in  1891,  describes  the  pre-Paleozoic  rocks  north  of  Lake 
Huron  as  having  been  subjected  in  certain  areas  to  vast  denudation 
and  decay  before  Paleozoic  time.  The  evidence  of  this  decay,  most 
frequently  found  in  granite,  consists  in  hollows,  pits,  irregular  ridges, 
and  even  small  caverns,  which  are  filled  with  Paleozoic  limestone. 
These  irregularities  are  regarded  as  having  been  formed  at  the  bot- 
tom of  the  deep  sea  by  solution.  Had  the  erosion  taken  place  on 
land  there  would  be  evidence  of  this  in  deeper  decay  in  the  substances 
of  the  rock  and  in  the  deposition  of  detrital  deposits  below  the  pure 
limestone,  which  in  many  cases  rests  directly  upon  the  pre-Paleozoic 
rocks. 
In  the  area  between  the  foot  of  Lake  Ontario  and  the  head  of 
Georgian  Bay  the  contact  of  the  Potsdam  sandstone  and  Black  River 
limestones  with  the  underlying  gneiss  and  quartzite  is  seen  at  many 
localities.  These  rocks  arc  generally  hard  and  fresh.  The  surface 
is  irregular,  and  the  whole  has  been  buried  beneath  the  horizontal 
Paleozoic  rocks. 
Many  of  the  long,  narrow  valleys  of  the  Archean  region  are  due  to 
the  decay  and  removal  of  wide  greenstone  dikes,  or  narrower  parallel 
