376  PRE-CAMBEIAN    GEOLOGY    OF    NORTH    AMERICA. 
typical  of  the  green  schist  portion  of  the  Basement  Complex  for  the 
region  as  a  whole,  and  it  was  recommended  that  his  name,  Keewatin, 
be  used,  on  the  ground  of  priority,  for  this  division  of  the  Basement 
Complex,  in  place  of  the  term  Mareniscan,  proposed  by  Van  Hise. 
The  succession  and  nomenclature  recognized  and  adopted  have  already 
been  given.     (See  p.  326.) 
From  the  foregoing  statements  it  might  be  concluded  that  Lake 
Superior  stratigraphy  below  the  Keweenawan  is  in  a  state  of  greater 
confusion  that  it  really  is,  for  a  closer  examination  of  the  various 
successions  shows  that  many  apparent  discrepancies  are  not  real,  if 
conclusions  are  not  extended  beyond  the  field  studied  in  each  case. 
While  there  is  still  some  difference  of  opinion  as  to  names  and  major 
correlation,  practically  all  who  have  any  detailed  knowledge  of  the 
Lake  Superior  and  Lake  Huron  regions  have  recognized  the  general 
succession  of  the  groups  and  formations  mentioned  in  the  joint  com- 
mittee report.  Confusion  has  resulted  because  the  conclusions  built 
up  from  a  study  of  a  small  part  of  the  region  have  been  assumed  to 
apply  to  the  whole,  because  the  groups  locally  have  been  wrongly 
placed  in  the  general  succession,  and  because  different  names  are 
used  for  the  same  thing.  The  Lake  Superior  region  is  so  large  that 
no  one  has  had  or  can  have  a  detailed  personal  knowledge  of  more 
than  a  small  part  of  it, 
DEFINITIONS      OF     "AZOIC,"     LAURENTIAN,     KEEWATIN,     ARCHEAN, 
HURONIAN,   ETC. 
Before  proceeding  further  it  will  be  well  to  summarize  the  litho- 
logical  characters  of  the  pre-Keweenawan  rocks  included  by  the  vari- 
ous writers  under  the  terms  applied  to  the  different  series  in  different 
districts,  although  this  will  result  in  repeating  to  some  extent  the  pre- 
ceding paragraphs.  It  is  here  much  less  easy  to  make  definite  state- 
ments than  in  the  case  of  the  Lake  Superior  sandstone  and  the 
Keweenawan. 
"Azoic? — As  used  by  Foster  and  Whitney  and  those  who  followed 
these  authors,  "Azoic  "  was  made  to  include  everything  below  the 
Keweenawan  except  the  rocks  which  are  plainly  igneous.  It  covered 
conglomerates,  quartzites,  slates,  and  marble,  as  well  as  the  gneisses. 
mica  schists,  hornblende  schists,  etc.;  that  is,  rocks  which  vary  in 
character  from  plainly  clastic,  as  conglomerates,  to  completely  crys- 
talline. The  granites,  syenites,  greenstones,  greenstone  slates,  iron 
ore,  jasper,  etc.,  were  regarded  as  igneous  rocks,  in  part  contempo- 
raneous with  and  in  part  newer  than  the  rocks  of  the  "Azoic  "  system, 
all  of  which  were  supposed  to  be  of  detrital  origin,  but  in  age  earlier 
than  the  Keweenawan. 
Laurentian. — As  used  by  most  of  the  earlier  Canadian  geologists, 
"  Laurentian  "  covers  most  of  the  light-colored  granites  and  coarse- 
