510  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
of  the  term  Agnotozoic  to  cover  the  Keweenaw,  an  Upper  Huronian 
and  equivalent  series  as  clearly  demand  that  it  shall  also  cover  other 
pre-Cambrian  clastic  series.  Once  started  on  the  downward  way  to- 
ward the  fundamental  complex  there  is  no  plane  at  which  to  stop  until 
this  is  reached. 
This  places  the  boundary  between  the  Proterozoic  and  Archean  at 
the  plane  placed  by  Selwyn  between  the  Lauren tian  and  Huronian.  In 
the  regions  in  which  Selwyn  and  most  other  Canadian  geologists  have 
studied,  they  in  general  find  no  unconformity  between  the  Huronian 
and  Laurentian.  It  has  been  seen  that  similar  apparently  conformable 
relations  and  gradations  obtain  in  various  areas  in  the  United  States. 
However,  in  many  cases,  as  has  been  seen,  there  are  easily  discover- 
able structural  breaks  between  the  Proterozoic  and  Archean. 
As  to  the  positions  of  Whitney  and  Wadsworth  and  Hunt,  my  con- 
clusions are  so  radically  different  that  little  need  be  said.  The  reasons 
for  the  conclusions  reached  have  appeared  in  the  summary  of  the  litera- 
ture and  in  this  discussion.  To  attempt  to  disprove  the  positions  of 
these  authors  would  be  merely  to  repeat  the  arguments  already  pre- 
sented. It  may,  however,  be  remarked  that  both  of  these  positions  can 
not  be  correct,  and  recently  Wadsworth  has  found  evidence  which  has 
led  him  to  change  entirely  his  views  from  those  expressed  in  the  "Azoic 
System."  One  maintained  the  absolute  indivisibility  and  complete 
lack  of  life  in  all  pre-Potsdam  rocks,  while  the  other  maintained  an 
invariable  aqueous  succession  of  pre-Cambrian  rocks,  consisting  of 
seven  different  series,  separated  by  unconformities.  The  position  here 
taken  is  in  some  degree  intermediate,  that  is  to  say,  there  is  abundant 
evidence  of  various  pre-Potsdam  clastic  series  which  bear  the  evidence 
of  life,  but  no  reason  in  the  facts  of  occurrence  nor  in  the  principles  of 
geology  which  indicates  for  all  regions  an  invariable  succession.  It  is 
not  worth  while  to  discuss  whether  in  1884,  the  time  when  Whitney 
and  Wadsworth's  account  of  the  Azoic  rocks  appeared,  evidence  was 
available  which  would  prove  the  divisibility  of  the  pre-Potsdam  rocks. 
If  any  one  desires  to  answer  this  question  tor  himself  he  will  consider 
only  that  part  of  the  literature  which  was  extant  prior  to  this  time. 
This  comparison  will  show  that  within  the  last  decade  has  appeared  a 
volume  of  evidence  upon  the  existence  of  pre-Potsdam  life  and  upon  the 
divisibility  of  the  pre-Cambrian  rocks  which  far  surpasses  that  obtained 
before.  At  the  present  time  the  evidence  in  favor  of  these  positions  is 
simply  overwhelming.  With  the  discouraging  view  taken  by  Whitney 
and  Wadsworth  as  to  the  state  of  pre-Cambrian  geology,  I  have  had 
no  sympathy.  They  said  that  the  chances  of  " having  at  some  future 
time  a  clear  understanding  of  the  geological  structure  of  northeastern 
North  America  would  be  decidedly  improved  if  all  that  has  been  writ- 
ten about  it  were  at  once  struck  out  of  existence."  Crude  methods 
have  frequently  led  to  crude  results,  but  often  even  in  unsatisfactory 
reports  are  contained  facts  which  serve  as  clews  to  later  workers.    Fur- 
