98  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
The  general  tendency  in  our  advance  in  knowledge  appears  to  be 
in  the  direction  of  extending  the  range  of  the  Paleozoic  downward, 
whether  under  the  old  name  of  Cambrian  or  under  some  other  name 
applied  to  a  new  system  defined  or  likely  to  be  defined  by  a  char- 
acteristic fauna;  and  under  Cambrian  or  such  new  system,  if  it  be 
admitted,  it  is  altogether  probable  that  the  Animikie  and  Kewee- 
nawan  rocks  must  eventually  be  included. 
The  introduction  of  the  term  Algonkian,  proposed  to  include  the 
recognizable  sedimentary  formations  below  the  Olenellus  zone  and 
their  igneous  equivalents,  is  believed  to  be  a  backward  step,  for  the 
following  reasons:  It  detaches  from  the  Paleozoic  great  masses  of 
conformable  and  fossiliferous  strata  beneath  an  arbitrary  plane  and 
unites  these  under  a  common  systematic  name  with  other  vast  series 
of  rocks,  now  generally  in  a  crystalline  condition;  it  includes  as  a 
mere  interlude  what,  in  the  region  of  the  Protaxis,  is  one  of  the 
greatest  gaps  known  to  geological  history ;  and  it  does  not  in  the  least 
degree  remove  the  difficulty  found  in  defining  the  base  of  the  Gren- 
ville  series. 
Dawson,31  in  1897,  in  an  account  of  the  physical  geography  and 
geology  of  Canada,  sketches  the  distribution  and  characters  of  the 
pre-Cambrian  rocks.  This  is  largely  a  general  summary  of  the 
present  state  of  knowledge  concerning  the  geology  of  Canada,  and 
will  therefore  not  be  fully  reviewed. 
Walcott,32  in  1899,  discusses  pre-Cambrian  fossiliferous  forma- 
tions of  North  America.  In  two  cases  only  have  fossils  of  undoubted 
organic  origin  been  shown  to  occur  in  formations  of  reasonably  cer- 
tain pre-Cambrian  age,  namely,  the  Grand  Canyon  of  Arizona,  and 
the  Belt  terrane  of  Montana.  The  Etcheminian  terrane  of  New 
Brunswick  and  Newfoundland  is  doubtfully  a  third  instance. 
A  brief  account  is  given  of  the  stratigraphy  of  each  of  the  areas  of 
pre-Cambrian  sedimentary  rocks.  No  new  points  appear  except  in 
the  description  of  the  Belt  terrane  of  Montana ;  the  account  of  the 
Belt  terrane  is  therefore  the  only  one  summarized  with  reference  to 
stratigraphy. 
The  Belt  terrane  of  Montana  covers  an  area  of  more  than  G,000 
square  miles  in  central  Montana.  The  principal  beds  of  the  terrane 
are  as  follows : 
Feet. 
Marsh  shales 300 
Helena  limestone 2,  400 
Empire  shales 600 
Spokane    shales 1,  500 
Greyson  shales 3,000 
Newland  limestone 2,  000 
Chamberlin  shales 1,  500 
Neihart  quartzite  and  sandstone 700 
12,  000 
