20  PKE-CAMBELAX    GEOLOGY   OF    NORTH   AMERICA. 
The  senior  author  has  favored  the  term  Proterozoic  (earlier  life)  as 
the  era  equivalent  of  the  Algonkian.  His  proposed  classification 
of  the  pre-Cambrian  as  given  in  the  first  edition  of  this  bulletin 
(Bulletin  No.  86)  and  repeated  in  the  Sixteenth  Annual  Report  of 
the  United  States  Geological  Survey,  except  that  "Agnotozoic  "  is 
omitted,  reads  as  follows :  a 
Era  or  group.  Period  or  system. 
Paleozoic Cambrian  and  others. 
Agnotozoic  or  Proterozoic Algonkian. 
Archean Archean. 
When  it  was  proposed  to  use  "Agnotozoic  "  or  Proterozoic  as  the 
equivalent  of  Algonkian  it  was  not  known  that  the  Archean  contained 
sediments. 
A  few  fossils  had  been  found  in  Algonkian  rocks.  Thus  there 
was  a  certain  basis  for  using  the  term  Proterozoic  as  equivalent  to 
Algonkian.  But  carbonaceous  shales,  limestones,  and  iron  formation 
rocks  extend  to  the  very  bottom  of  the  known  geological  column, 
suggesting  existence  of  life  in  the  earliest  rocks.  However,  the  life 
remains  of  the  pre-Cambrian  are  far  too  scant  to  warrant  any  attempt 
at  subdivision  of  the  pre-Cambrian  on  the  "  zoic  "  basis.  The  major 
classification  of  the  pre-Cambrian  has  been  made  upon  a  physical  and 
not  a  paleontological  basis.  For  this  reason,  therefore,  the  writers 
prefer  to  use  the  terms  Archean  and  Algonkian,  without  separate 
"  zoic  "  equivalents. 
Our  proposed  classification  of  the  pre-Cambrian  is  as  follows : 
{One  or  more  series  in  various  geological  prov- 
inces, separated  by  unconformities.     To  these 
series  local  names  are  applicable. 
Unconformity. 
{Keewatin. 
Eruptive  unconformity. 
Laurentian. 
Chamberlin  and  Salisbury,6  in  their  text-book  of  geology,  have 
proposed  the  divisions  Proterozoic  and  Archseozoic  for  the  rocks 
which  we  here  call  Algonkian  and  Archean,  but  such  "  zoic  "  division 
is  not  founded  on  evidence  furnished  by  fossils  and  represents  a  hope 
of  the  future  rather  than  achieved  results.  It  seems  probable  from  the 
great  physical  contrasts  in  the  Archean  and  Algonkian  that  this 
proposed  "  zoic  "  division  would  be  justified  if  we  could  know  the 
life  of  these  two  eras,  though  this  is  yet  a  speculative  belief  based 
upon  general  principles. 
•  Sixteenth  Ann.  Kept,  (for  1894-95)  U.  S.  Geol.  Survey,  pt.  1,  1896,  p.  762. 
b  Chamberlin,    T.    C,    and    Salisbury,    R.    D.,    Text-book    of   geology,    vol.    2,    1906,    pp. 
133-217 
