﻿GENERAL 
  CLASSIFICATION 
  OF 
  GEOLOGIC 
  TEVIE 
  AND 
  STRATA. 
  135 
  

  

  From 
  this 
  it 
  results, 
  that, 
  as 
  we 
  go 
  southward 
  from 
  Lake 
  On- 
  

   tario, 
  we 
  ascend 
  in 
  vertical 
  altitude 
  and 
  also 
  in 
  the 
  geologic 
  

   column. 
  Our 
  youngest 
  Palaeozoic 
  rocks, 
  which 
  are 
  Lower 
  Car- 
  

   boniferous, 
  are 
  near 
  the 
  Pennsylvania 
  boundary. 
  

  

  These 
  physiographic 
  features 
  are 
  well 
  shown 
  on 
  the 
  accom- 
  

   panying 
  relief 
  map 
  of 
  New 
  York. 
  

  

  For 
  a 
  detailed 
  discussion 
  of 
  the 
  geography 
  of 
  New 
  York 
  see 
  

   Examination 
  bulletin 
  11, 
  University 
  of 
  the 
  State 
  of 
  New 
  York, 
  

   by 
  Wm. 
  Morris 
  Davis. 
  ' 
  

  

  GENERAL 
  CLASSIFICATION 
  OF 
  GEOLOGIC 
  TIME 
  

  

  AND 
  STRATA 
  

  

  It 
  must 
  be 
  realized 
  by 
  the 
  student 
  at 
  the 
  outset 
  that 
  all 
  classi- 
  

   fication 
  is 
  to 
  some 
  extent 
  arbitrary. 
  There 
  was 
  throughout 
  the 
  

   earth 
  as 
  a 
  whole 
  a 
  continuous 
  process 
  of 
  erosion 
  and 
  sedimenta- 
  

   tion 
  and 
  a 
  continuous 
  chain 
  of 
  life. 
  Locally, 
  through 
  changes 
  of 
  

   level, 
  sedimentation 
  was 
  varied 
  and 
  life 
  interrupted 
  from 
  time 
  to 
  

   time. 
  For 
  convenience 
  in 
  discussion, 
  a 
  scheme 
  of 
  arrangement 
  

   has 
  been 
  adopted 
  which 
  is 
  based 
  on 
  the 
  more 
  conspicuous 
  of 
  

   these 
  breaks 
  in 
  life 
  and 
  sedimentation. 
  

  

  Accoo'ding 
  to 
  the 
  classification 
  most 
  generally 
  accepted, 
  the 
  

   principal 
  divisions 
  of 
  the 
  geologic 
  time 
  scale 
  are 
  called 
  aeons 
  or 
  

   times 
  and 
  designated 
  by 
  the 
  following 
  names 
  which 
  are 
  based 
  on 
  

   the 
  principal 
  features 
  of 
  life 
  development 
  : 
  

  

  Cenozoic, 
  latest 
  time, 
  characterized 
  by 
  forms 
  closely 
  related 
  

   to 
  those 
  of 
  the 
  present 
  day. 
  

  

  Mesozoic, 
  middle 
  time 
  of 
  life 
  development. 
  

  

  Palaeozoic, 
  early 
  time; 
  ancient 
  forms 
  of 
  life 
  well 
  developed. 
  

  

  Proterozoic 
  or 
  Agnotozoic, 
  life 
  not 
  well 
  known 
  as 
  yet. 
  

  

  Archaean 
  time 
  of 
  the 
  most 
  ancient 
  rocks 
  with 
  only 
  suggestive 
  

   traces 
  of 
  life. 
  

  

  