SUMMARY   OF   GENERAL   LITERATURE.  95 
The  Olenellus  fauna  includes  Spongiae,  Hydrozoa,  Actinozoa,  Echi- 
nodermata,  Annelida,  Brachiopoda,  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  of  it  known  prove  little  of  its  character,  but 
they  show  that  life  existed  in  a  period  far  preceding  Lower  Cam- 
brian time,  and  they  foster  the  hope  that  abundant  remains  will  yet 
be  discovered. 
Dana,24  in  1892,  gives  the  following  as  the  philosophical  divisions 
of  pre-Cambrian  times,  although  the  early  physical  and  biological 
conditions  of  the  globe  are  not  within  the  range  of  observation : 
I.  The  Astral  eon,  as  it  has  been  called,  or  that  of  liquidity. 
II.  The  Azoic  eon,  or  that  without  life. 
1.  The  lithic  era,  commencing  with  completed  consolidation; 
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  Archeozoic  eon,  or  that  of  the  first  life. 
1.  The  era  of  the  first  plants;  the  algse  and  later  the  aqua- 
tic fungi  (bacteria)  ;  commencing  possibly  with  the  mean 
surface  temperature  of  the  ocean  about  180°  F. 
2.  The  era  of  the  first  animal  life ;  the  protozoans,  and  forms 
related  to  the  embryos  of  higher  invertebrate  species,  com- 
mencing possibly  with  the  mean  surface  temperature  of 
the  waters  about  120°  F.,  and  ending  with  90°  F.  or  below. 
While  these  divisions  mark  off  great  steps  in  the  progress  of  the  de- 
veloping earth,  the  rocks  bear  no  marks  of  them  that  can  be  distin- 
guished. 
The  Huronian  period  covered  probably  much  of  Archeozoic  time, 
and  this  is  all  that  can  be  said  in  the  way  of  correlation.  It  is  well  to 
note  here  that  if  the  Eozoon  is  really  animal  in  origin  the  "  Lauren- 
tian  "  rocks  of  Canada  in  which  it  occurs  must  be  Huronian  or  the 
later  of  Archean  terranes. 
Van  Hise,25  in  1892,  summarizes  knowledge  to  date  on  the  pre- 
Cambrian  areas  of  North  America  and  discusses  the  nature  and  cor- 
relation of  the  pre-Cambrian  series.  This  is  the  first  attempt  to  make 
a  concise  statement  of  this  complex  subject.  The  present  bulletin  is 
a  restatement  of  the  subject  in  the  light  of  the  studies  which  have 
been  made  since  1892. 
Williams,20  in  1894,  discusses  the  distribution  of  the  ancient  vol- 
canic rocks  along  the  eastern  border  of  North  America,  from  New- 
