vanhisk.1  DISCUSSIONS   OF   PRINCIPLES.  4G9 
tions;  (2)  at  the  line  of  an  unconformable  contact  between  any  member 
of  the  Cambrian  group  and  the  subjacent  Algonkian  or  Arckean;  (3) 
at  the  line  of  unconformable  contact,  which  is  the  base  of  the  Olenellus 
zone. 
Placed  in  the  Algonkian  under  this  definition  are  11,000  feet  of 
quartzites,  conformably  below  the  Olenellus,  in  the  Wasatch;  10,000 
feet  of  argillites,  sandstones,  quartzites,  and  conglomerates,  conforma- 
bly beneath  the  Olenellus,  in  British  Columbia;  12,000  feet  of  sand- 
stones, shales,  and  limestones  uneonformably  beneath  the  lowest  known 
Cambrian,  in  the  Grand  canyon  of  Colorado;  a  similar  series  of  rocks 
uneonformably  beneath  the  Cambrian  in  Llano  county,  Texas;  aperies 
uneonformably  below  the  Upper  Cambrian  in  the  Adirondacks;  and 
the  locks  of  St.  Marys  and  Placentia  bay,  Newfoundland,  which  are 
uneonformably  below  Lower  Cambrian  strata.  In  the  Grand  canyon, 
in  a  bed  of  dark  argillaceous  shale,  3,550  feet  from  the  summit  of  the 
section,  was  found  a  small  Patelloid  or  Discinoid  shell,  a  fragment  of 
what  appears  to  be  the  pleural  lobe  of  a  segment  of  a  trilobite,  and  an 
obscure,  small  Hyolithes,  in  a  layer  of  bituminous  limestone.  In  layers 
of  limestone,  still  lower  in  the  section,  an  obscure  Stromatoporoid  form 
occurs  in  abundance.  These  fossils  indicate  a  fauna,  but  do  not  tell 
what  it  is. 
The  Olenellus  fauna  includes  Spongias,  Hydrozoa,  Aetinozoa,  Echi- 
nodermata,  Annelida,  Braehiopoda,  Lamellibranchiata,  Gasteropoda, 
Pteropoda,  Crustacea,  and  Trilobita.  The  abundance  of  the  Olenellus 
fauna  shows  that  the  life  in  the  pre-Olenellus  seas  was  large  and  varied. 
The  few  traces  known  of  it  prove  little  of  its  character,  but  they  prove 
that  life  existed  in  a  period  far  preceding  Lower  Cambrian  time,  and 
they  foster  the  hope  that  it  is  only  a  question  of  search  and  favorable 
conditions  to  discover  it. 
Dana,23  in  1892,  gives  the  following  as  the  philosophical  divisions  of 
pre-Cambrian  times,  although  the  early  physical  and  biological  condi- 
tions of  the  globe  are  not  within  the  range  of  observation : 
I.  The  Astral  a3on,  as  it  has  been  called,  or  that  of  liquidity. 
II.  The  Azoic  ason,  or  that  without  life. 
1.  The  Lithie  era,  commencing  with  completed  consolida- 
tion;, the  time  when  lateral  pressure  for  crust  disturbance 
and  mountain-making  was  initiated,  and  when  metamorphic 
work  began. 
2.  The  Oceanic  era,  commencing  with  the  ocean  in  its  place; 
oceanic  waves  and  currents  and  embryo  rivers  beginning 
their  work  about  emerged  and  emerging  lands,  and  the 
tides,  the  retarding  of  the  earth's  rotation. 
III.  The  Arclneozic  aion,  or  that  of  the  first  life. 
1.  The  era  of  the  first  Plants;  the  Algae  and  later  the  aqua- 
tic Fungi  (Bacteria);  commencing  possibly  with  the  mean 
surface  temperature  of  the  ocean  about  180°  F. 
