GENERAL  ACCOUNT    OF    THE   PRE-CAMBRIAN    ROCKS.  21 
Emile  Haug,°  realizing  the  difficulty  of  dividing  the  pre-Cambrian 
on  the  "  zoic  "  basis,  has  proposed  to  use  only  a  single  "  zoic  "  term 
for  all  of  the  pre-Cambrian  rocks.  For  this  term  he  has  chosen  the 
word  "Agnotozoic,"  which  he  separates  into  Archean  and  Algonkian. 
If  Professor  Haug's  plan  be  followed,  it  seems  to  us  that  the  prefer- 
able term  for  this  place  is  Proterozoic  rather  than  "Agnotozoic.*' 
However,  since  the  proper  choice  of  "  zoic  "  terms  can  be  made 
only  by  future  development  of  knowledge,  and  there  is  no  consensus 
of  opinion  on  the  matter,  we  shall  avoid  introducing  the  "  zoic  " 
nomenclature  into  this  discussion,  confining  ourselves,  as  has  been 
said,  for  the  major  subdivisions  of  the  pre-Cambrian  to  the  terms 
Algonkian  and  Archean,  the  forms  of  which  correspond  with  the 
physical  basis  upon  which  the  separation  is  actually  made. 
It  does  not  follow  from  emphasis  on  structural  and  physical  char- 
acteristics rather  than  paleontological  differences  that  this  classifica- 
tion has  any  less  value  than  at  later  periods.  As  Chamberlin  ex- 
presses it:-B 
The  groups  Paleozoic,  Mesozoic,  and  Cenozoic  are  not,  in  the  conception  of 
some  of  us,  defined  by  a  distinct  kind  of  life,  as  in  the  case  of  some  of  the  minor 
horizons,  for  the  life  fits  better  the  idea  of  a  gradation  than  of  a  distinct  sepa- 
ration. These  great  divisions  are  rather,  as  I  see  it,  at  least,  great  historic 
movements  fundamentally  dependent  upon  dynamic  events,  than  paleontological 
divisions.  Originally  they  were  supposed  to  be  separated  by  universal  catas- 
trophies  to  life,  and  their  distinctness  was  due  rather  to  the  intervention  of  the 
catastrophe  than  to  the  different  quality  of  the  life,  which  is  merely  seized  upon 
as  a  characteristic  suited  to  nomenclature. 
In  this  sense  the  Algonkian  system  is  characterized  by  essentially 
the  same  criteria  as  the  Paleozoic  and  the  Mesozoic. 
The  Algonkian  includes  the  major  part  of  the  pre-Cambrian  sedi- 
mentary rocks — practically  all  to  which  ordinary  stratigraphic  meth- 
ods may  apply — though  it  also  contains  sediments  so  deformed  and 
metamorphosed  that  their  stratigraphy  can  not  be  deciphered.  The 
Archean  is  the  basement  complex,  perhaps  including  several  series  or 
groups,  upon  which  the  Algonkian  rests,  so  far  as  known,  with  uncon- 
formity. It  includes  massive  igneous  rocks,  acidic  and  basic,  crystal- 
line schists  and  gneisses  derived  from  them,  large  masses  of  schists 
and  gneisses  of  unknown  origin,  and  relatively  small  masses  and 
shreds  of  fragmental  formations  so  highly  metamorphosed  and  so 
closely  associated  with  the  schists  and  gneisses  in  structure  and  age 
that  they  can  not  yet  be  practicably  separated  in  mapping. 
The  Algonkian  is  characterized  by  well-assorted  fragmental  and 
chemical  sediments  giving  evidence  of  extensive  decomposition  of 
land  areas  and  of  the  passage  of  normal  cycles  of  erosion.  Igneous 
rocks  are  abundantly  present,  but  for  the  most  part  arc  subordinate 
a  Traite  do  Geologie,  I,  Los  Phenomones  geologiques,  Paris,   1907,   p.  22 
6  Personal  communication,   January  6,   1908. 
