288  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
At  Black  Bay  the  Keweenawan  sediments  are  interbedded  with 
basic  flows  and  contain  pebbles  of  basic  eruptives  and  acidic  porphy- 
ries, showing  that  at  this  locality  the  volcanic  outflows  of  Keweena- 
wan time  occurred  before  the  deposition  of  the  sediments. 
At  the  mouth  of  Nipigon  Bay  are  gabbro,  amygdaloidal  lava,  and 
red  rock,  which  are  strongly  believed  to  be  a  series  correlative  with 
the  Beaver  Bay  group. 
East  of  Nipigon  Bay  Van  Hise  finds  a  complex  of  spheroidal 
greenstones,  green  schists,  gneisses,  and  granites,  showing  the  usual 
intricate  relations  of  the  Archean.  Also  at  intervals  east  as  far  as 
Schreiber  are  exposures  of  Animikie  and  Keweenawan,  capped  by 
columnar  jointed  diabase  with  the  usual  steep  north  faces  and  gentle 
dips  toward  the  lake.  In  general  there  is  a  thin  conglomerate  at  the 
base  of  the  Animikie,  although  in  places  this  is  lacking. 
From  Steel  River  to  Heron  Bay  is  a  greenstone  and  green  schist 
complex,  in  all  respects  analogous  to  that  of  the  Marquette  district — 
mashed  greenstones  forming  schists,  banded  slaty  phases,  greenstone 
tuffs,  and  conglomerates. 
From  south  of  Pic  River  nearly  to  Pukaskwa  River  Van  Hise  fol- 
lows Logan  and  Irving  in  making  all  the  area  Laurentian  in  the 
sense  of  being  Archean  and  including  later  eruptives.  He  can  see  no 
criteria  for  the  separation  into  Laurentian  and  Huronian,  as  there 
is  no  sharp  line  separating  the  areas  of  greenstones  and  green  schists 
and  the  massive  granites. 
Batchawana  Bay  is  unique  in  showing  four  geological  systems — 
(1)  Archean  granite  gneiss  schist,  (2)  Huronian  graywacke.  (3) 
Keweenawan  amygdaloids,  and  (4)  Cambrian  sandstones.  Batcha- 
wana Bay  is  probably  structurally  a  minor  syncline. 
Clements  finds  about  Lake  Nipigon  the  following  rocks:  (1) 
Fairly  massive  greenstone,  which  very  commonly  shows  well-devel- 
oped ellipsoidal  parting.     With  this  are  associated  schistose  phases. 
(2)  Derived  from  the  greenstones,  and  stratigraphically  overlying 
them,  is  a  series  of  sediments  consisting  of  conglomerates,  gray- 
wackes,  and  slates,  the  first  two  predominating.  With  these  at  one 
locality  are  bands  of  hematite  and  jasper,  forming  an  iron-bearing 
formation.  These  divisions  are  closely  related  and,  since  they  repre- 
sent the  Archean  of  the  Vermilion  district,  are  classed  as  Archean. 
As  a  whole  they  have  a  green  color  and  are  more  or  less  schistose. 
(These  are  the  rocks  which  Bell  has  designated  green  schists  and 
classified  as  of  Huronian  age.)  These  rocks  are  cut  through  by 
numerous  dikes  of  granite,  which  are  offshoots  of  the  massive  granite 
that  occurs  in  various  areas.  (3)  At  Vermilion  Bay  he  finds  a  lim- 
ited occurrence  of  slates,  graywackes,  and  conglomerates  which  are 
well  bedded  and  stand  approximately  on  edge,  with  east-west  strike. 
These  sediments  overlie  and  are  younger  than  a  greenstone  which  is 
