58  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
Macfarlane,14  in  1869,  describes  at  Thunder  cape  a  series  of  inter- 
stratiiied  argillaceous  and  white  and  red  dolomitic  sandstones,  which 
had  been  disturbed  and  eroded  before  the  flow  appeared  which  forms 
the  summit  rock  of  the  cape. 
Bell,15  in  1870,  gives  an  account  of  the  geology  of  the  northwest 
coast  of  lake  Superior  and  the  Mpigon  district.  The  copper-bearing 
rocks  are  divided  into  a  lower  group  and  an  upper  group,  and  each  of 
these  groups  separated  into  several  divisions.  In  the  upper  group  only 
is  found  interbedded  trap.  Different  portions  of  this  series  are  found 
overlying  unconformably  in  certain  places  the  Laurentian  and  in 
others  the  Huronian;  and  the  great  trap  overflow  which  crowns  Thun- 
der cape  rests  in  various  places  unconformably  upon  different  mem- 
bers of  both  the  upper  and  lower  groups  of  the  Upper  Copper-bearing 
series.  On  account  of  the  great  thickness  of  this  series,  the  absence 
of  fossils,  the  prevalence  of  marls  and  sandstones  charged  with  red 
oxide  of  iron,  and  of  basalts,  amygdaloids,  and  trap  rocks,  and  various 
zeolites  and  native  copper,  this  series  is  considered  as  probably  of 
Permian  or  Triassic  age.  Between  the  margin  of  the  Upper  Copper, 
bearing  rocks  on  Thunder  bay  and  the  Laurentian  range,  all  the  country 
not  occupied  by  the  syenitic  areas  appear  to  be  composed  of  rocks  of 
the  Huronian  series,  consisting  of  diorites,  dioritic  conglomerates,  horn- 
blendic  and  fine  grained  micaceous  slates,  with  some  quartzites. 
Bell,16  in  1872,  finds  in  the  country  north  of  lake  Superior,  between 
Mpigon  and  Michipicoten  rivers,  both  Laurentian  and  Huronian  rocks. 
The  former  includes  gneisses  and  granites,  and  the  latter  includes 
slates,  conglomerates,  massive  and  schistose  diorites,  fine  grained 
gneisses,  mica-schists,  micaceous,  hornblendic,  chloritic,  feldspathic 
and  epidotic  schists,  slates,  granites,  and  iron  ore.  The  Huronian  rocks 
dip  in  various  directions.  At  White  river  hornblendic  schist  and  light 
gray  gneiss  are  inter  stratified  with  massive  granitic  gneiss,  and  similar 
schists  appear  to  rest  conformably  upon  massive  gneisses  for  a  long 
way  north  of  the  river. 
Bell,17  in  1872,  finds  in  the  country  between  lake  Superior  and  the 
Albany  river  areas  of  Laurentian  and  Huronian  rocks.  Between 
Mousewake  lake  and  Martins  falls  bands  of  gneiss  are  inter  stratified 
with  the  schists,  and  just  at  Martins  falls  the  latter  have  become  en- 
tirely replaced  by  red  and  gray  gneisses,  apparently  showing  a  con- 
formable passage  from  the  Huronian  into  the  Laurentian  rocks.  A 
similar  blending  of  these  formations  was  noticed  last  year  in  the  neigh- 
borhood of  White  lake. 
Selwyn,18  in  1873,  finds,  between  Mille  Lacs  and  Separation  lake  and 
the  lake  of  the  Woods,  a  series  of  parallel  bauds  of  schistose  and  slaty 
layers  where  hitherto  was  supposed  to  be  almost  exclusively  the 
Laurentian  gneiss.  The  facts  observed  lead  to  the  conclusion,  as 
stated  by  Bell,  that  the  two  series  are  in  conformable  sequence;  yet  it 
is  far  from  improbable  that  this  apparent  conformity  is  only  local  and 
