van  msE.]  DISCUSSIONS    OF    PRINCIPLES.  475 
Recently  Irving  has  proposed  that  there  he  placed  below  the  Paleo- 
zoic group  another  group  of  coordinate  value,  for  which  the  term  Ag- 
notozoic  or  Eparchean  is  suggested.  This  term  cuts  out  of  the  Archean 
a  large  class  of  rocks  which  have  before  been  here  included.  Finally, 
the  name  Algonkian  has  been  brought  forward  by  the  United  States 
Geological  Survey  for  a  systematic  place  opposite  Agnotozoic  or  Epar- 
chean. 
In  the  following  discussion,  as  stated  in  the  introduction,  Cambrian 
is  defined  as  extending  downward  to  the  base  of  the  Olenellus  fauna. 
The  pre-Olenellus  elastics  and  their  equivalent  crystallines  are  called 
Algonkian,  and  the  completely  crystalline  rocks  below  the  Algonkian 
are  denominated  Archean.  The  reasons  for  these  usages  will  appear 
in  the  following  pages;  The  stratigraphieal  te^ms,  group,  system,  and 
series  correspond  with  the -usage  proposed  by  the  International  Geo- 
logical Congress.  The  same  is  true  of  the  chronological  divisions,  era 
and  period.     Formation  is  a  lithological  subdivision  of  a  series. 
THE  CHARACTER  OE  THE  ARCHEAN. 
From  the  review  of  the  literature  it  is  plain  that  there  is  an  essential 
unity  in  the  character  of  the  complex  of  rocks  which  is  the  oldest  known 
in  America.  This  statement  covers  all  the  areas  in  which  the  rocks 
are  demonstrated  to  be  exceedingly  ancient.  It  includes  the  basal 
complex  of  Arizona,  between  which  and  the  Tonto  sandstone  is  a  clastic 
system  15,000  feet  thick,  separated  into  three  series  by  unconformities, 
and  these  again  separated  from  the  Tonto  above  and  the  basal  complex 
below  by  great  unconformities;  it  includes  the  basal  complex  of  the 
Wasatch  and  certain  of  the  ranges  of  Nevada,  between  which  and  the 
Olenellus  Cambrian  is  a  great  unconformity  and  a  thick  series  of  quartz- 
ites;  it  includes  the  basal  complex  of  southwestern  Montana,  between 
which  and  the  Olenellus  Cambrian  is  12,000  feet  of  unaltered  slates  and 
a  thick  series  of  crystalline  rocks  of  clastic  origin,  the  two  being  prob- 
ably separated  by  a  great  unconformity;  it  includes  the  basal  complex 
of  Texas,  between  which  and  the  Cambrian  is  an  unconformity,  at  least 
one  and  perhaps  two  thick  series  of  clastic  rocks;  it  includes  the  basal 
complex  of  the  lake  Superior  region,  between  which  and  the  Cambrian  is 
an  enormous  system  of  elastics  many  thousands  of  feet  thick,  separated 
by  unconformities  into  three  series,  and  the  whole  bounded  above  and 
below  by  unconformities ;  it  includes  the  basal  complex  of  the  north 
shore  of  lake  Huron,  between  which  and  the  Cambrian  is  a  clastic  series 
18,000  feet  thick,  bounded  above  and  below  by  unconformities;  it  in- 
cludes the  basal  complex  of  the  original  Laurentian  area,  between  which 
and  the  Cambrian  is  a  clastic  series  estimated  to  be  many  thousands  of 
feet  thick;  it  includes  the  basal  complex  of  Hudson  bay,  between  which 
and  the  Cambrian  are  almost  certainly  two,  and  perhaps  three  series 
of  elastics  separated  by  unconformities ;  it  probably  includes  the  basal 
complex  of  Newfoundland,  between  which  and  the  Olenellus  Cambrian 
