194  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  80. 
ter  subserved  by  using  the  term  Algonkian  to  coverall  the  clastic 
series  between  the  Fundamental  Complex  and  Cambrian,  and  to  retain 
Archean  as  a  term  of  coordinate  value  with  this  to  cover  the  basal  com- 
plex. If  it  shall  turn  out  that  the  writer  is  correct  as  to  the  position 
of  the  Coutchiching,  the  base  of  the  Lower  Huronian,  not  the  base  of 
the  Coutchiching,  is  the  important  horizon  to  mark.  More  evidence  is 
desirable  for  the  application  of  strati  graphical  methods  to  the  promi- 
nent structure  of  the  Coutchiching,  since,  in  many  respects  this  struc- 
ture has  the  characters  of  an  induced  one.  Lawson  recognizes  a  true 
physical  break  at  the  base  of  the  Keewatin,  not  at  the  base  of  the 
Coutchiching.  The  break  between  the  Coutchiching  and  the  granite- 
gneiss  is  one  which  is  also  found  between  the  granite-gneiss  and  Kee- 
watin. It  is  not  a  structural  horizon,  but  an  eruptive  contact.  Upon 
the  other  hand,  a  great  mass  of  evidence  goes  to  show  that  there  is  at 
the  base  of  the  Keewatin  a  persistent  structural  plane  which  is  recog- 
nizable throughout  the  lake  Superior  region. 
Selwyn  and  N.  H.  Winchell  maintain  that  the  Keweenawan  and 
Animikie  are  properly  Cambrian.  Whether  the  term  Cambrian  shall 
be  so  extended  downward  as  to  cover  two  great  unconformities  and 
two  additional  rock  series  of  very  great  thickness  is  purely  a  matter  off 
policy  and  of  nomenclature,  which  is  more  fully  discussed  in  another 
place.  While  it  is  of  primary  importance  that  an  agreement  shall  be 
reached  as  to  the  actual  rock  successions  in  the  lake  Superior  region, 
it  is  but  a  secondary  matter  as  to  the  names  which  shall  be  applied  to 
them.  That  fossils  are  found  in  the  Huronian  is  not  sufficient  reason 
for  extending  the  Cambrian  downward  indefinitely.  That  the  evi- 
dences of  abundant  life  are  here  found,  has  been  long  known.  Many 
of  the  thick  beds  of  slates  heretofore  called  Huronian,  on  the  south 
shore  of  lake  Superior,  not  only  contain  graphitic  material,  but  a  con- 
siderable percentage  of  hydrocarbons,  not  infrequently  becoming  graph- 
itic or  carbonaceous  schists.  In  the  Animikie,  on  the  north  shore  of 
lake  Superior,  Ingall  finds  abundant  carbon,  and.  it  is  said  that  in 
certain  mines  and.  openings  rock  gas  forms  in  considerable  amount. 
Also  small  quantities  of  rock  may  even  be  obtained  which  will  burn,  j 
These  substances  must  result  from  the  ordinary  processes  which  pro- 
duced rock  gas  and  coal  in. the  rocks  of  far  later  age.  Also  the  great 
beds  of  iron  carbonate  are,  to  many,  evidence  of  abundant  life.  In  the 
Sioux  quartzites  one  generally  accepted  fossil  has  been  discovered  by 
IS".  H.  Winchell.  A  discovery  of  a  fossil  has  been  announced  by  Selwyn 
as  occurring  in  the  Animikie.  It  is  a  hope  that  in  the  future  numerous 
other  fossils  will  be  found  in  this  series,  so  that  we  may  have  the  assist- 
ance of  paleontology  in  lake  Superior  stratigraphy.  Until,  however, 
a  fauna  is  known  in  these  regions  which  is  distinctly  Cambrian,  the 
discovery  of  life  or  of  certain  fossils  in  the  Keweenawan  and  Huronian 
rocks  is  wholly  insufficient  evidence  for  placing  them  with  the  Cambrian 
We  then  have  in  the  lake  Superior  region  the  following  successions- 
and  correlations  for  the  pre-Cambrian  rocks: 
