vanhise.]  DISCUSSIONS    OF    PRINCIPLES.  513 
of  dynamic  action,  the  particles  of  quartz  not  even  being  arranged  with 
their  longer  axes  in  the  same  direction,  and  the  induration  being  wholly 
due  to  the  process  of  renewed  growth  and  cementation.  Yet  this  and 
the  adjacent  rocks  have  been  buried  under  the  entire  thickness  of  the 
Upper  Huronian  and  the  Keweenawan  series  many  thousands  of  feet 
and  subjected  to  a  pressure  beyond  the  crushing  strength  of  any  rock, 
a  condition  in  which  they  must  have  beeu  latently  plastic.  Rocks  as 
late  as  Devonian  in  the  Appalachians  have  become  so  completely  crys- 
talline that  not  one  vestige  of  the  original  fragmental  material  remains. 
Contrasting  with  this  occurrence  are  the  Chuar,  Grand  Canyon,  and 
Keweenaw  series,  all  wholly  unaltered,  yet  pre-Cambrian. 
No  one  would  think  of  maintaining  that  in  post-Cambrian  time  a  rock 
of  a  certain  composition  is  of  a  definite  age;  neither  would  any  one 
think  of  referring  a  rock  to  the  Devonian,  Silurian,  or  Cambrian  upon 
the  degree  of  its  crystallization.  To  suppose  that  the  plane  of  the  basal 
Cambrian  is  a  magic  one,  below  which  new  conditions  of  sedimentation 
prevailed  and  an  entirely  different  set  of  principles  apply  in  stratig- 
raphy, is  to  assume  a  revolution  in  the  conditions  of  the  world  at  this 
time  for  which  there  is  not  one  particle  of  warrant.  Those  who  believe 
in  evolution  must  believe  that  for  eras  of  time  before  the  Cambrian 
there  were  cycles  of  deposition  of  the  various  classes  of  sedimentary 
rocks  and  the  slow  evolution  of  life  to  the  high  degree  of  perfection 
and  the  great  variety  of  types  including  all  important  branches  except 
the  vertebrates  found  in  the  Olenellus  fauna. 
It  may  be  said  that  the  foregoing  applies  equally  well  to  the  separa- 
tion of  the  Algonkian  and  Archean.  Revolutionary  methods  can  not 
be  applied  here  more  than  elsewhere.  To  this  it  can  only  be  said  that 
this  plane  is  the  most  remote  and  difficult  to  define  of  any.  It  may  be 
that  it  is  wrongly  defined.  Without  question  it  will  in  the  future  be 
much  more  accurately  defined.  Rocks  now  placed  in  the  Archean  will 
be  found  to  be  Algonkian,  just  as  series  are  being  found  to  be  Cam- 
brian, Silurian,  or  Devonian  in  the  Appalachians  which  have  commonly 
been  regarded  as  Huronian  or  Laurentian.  While  the  distinctions 
made  may  not  be  complete,  they  are  based  upon  the  knowledge  availa- 
ble, are  not  dogmatic,  and  do  not,  it  appears  to  the  writer,  contradict 
the  laws  of  geology.  The  law  of  uniformity,  if  rightly  understood,  does 
not  imply  that  the  causes  now  at  work  have  always  had  the  same  rela- 
tive value.  When  the  laws  of  geologic  forces  are  fully  comprehended, 
it  will  be  found  that  each  is  not  absolutely  uniform  in  power,  but  that 
each  involves  variables.  These  variables  may  be  so  small  that  the 
cumulative  change  in  the  effect  in  any  case  may  not  be  discoverable  in 
an  epoch  or  even  in  a  period ;  but  that  the  amount  of  this  effect  per- 
ceptibly changed  in  eras,  can  not  be  doubted.  A  standard  clock  if 
observed  for  a  day  may  seem  to  run  with  an  invariable  and  correct 
Irate,  but  if  observed  long  enough  it  is  found  to  lose  or  gain,  and  this 
not  regularly.  The  law  of  its  variation  may  finally  be  partly  ascer- 
Bull.  86 33 
