﻿18 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Each 
  of 
  these 
  time 
  divisions 
  is 
  farther 
  divided 
  into 
  great 
  eras, 
  

   those 
  of 
  Paleozoic 
  time 
  being 
  given 
  in 
  the 
  annexed 
  table. 
  Each 
  

   era 
  is 
  in 
  general 
  divisible 
  into 
  three 
  periods 
  of 
  time, 
  the 
  early, 
  mid- 
  

   dle, 
  and 
  later, 
  for 
  wiiich 
  the 
  prefixes 
  paleo 
  (or 
  eo), 
  meso 
  and 
  neo 
  are 
  

   used. 
  The 
  farther 
  division 
  of 
  the 
  periods 
  is 
  into 
  epochs. 
  

  

  During 
  the 
  continuance 
  of 
  each 
  great 
  time 
  division 
  of 
  the 
  geo- 
  

   logic 
  history 
  of 
  the 
  earth, 
  more 
  or 
  less 
  extensive 
  rock 
  systems 
  were 
  

   deposited, 
  wherever 
  the 
  conditions 
  were 
  favorable. 
  Thus 
  the 
  Paleo- 
  

   zoic 
  rock 
  system 
  is 
  that 
  deposited 
  during 
  Paleozoic 
  time. 
  That 
  

   part 
  of 
  the 
  Paleozoic 
  rock 
  system 
  which 
  was 
  deposited 
  during 
  the 
  

   Siluric 
  era, 
  is 
  called 
  the 
  Siluric 
  rock 
  series, 
  and 
  similarly, 
  the 
  name 
  

   of 
  each 
  of 
  the 
  other 
  great 
  eras 
  is 
  also 
  applied 
  to 
  the 
  rock 
  series 
  

   deposited 
  during 
  its 
  continuance. 
  In 
  like 
  manner 
  each 
  geologic 
  

   period 
  has 
  its 
  corresponding 
  group 
  of 
  rocks 
  deposited 
  during 
  its 
  con- 
  

   tinuance. 
  These 
  rock 
  groups 
  and 
  their 
  farther 
  subdivision 
  into 
  

   stages 
  have, 
  in 
  New 
  York, 
  received 
  local 
  names, 
  the 
  name 
  of 
  the 
  

   locality 
  where 
  the 
  rocks 
  are 
  best 
  developed 
  being 
  selected. 
  The 
  

   rocks 
  formed 
  during 
  Proterozoic 
  and 
  Azoic 
  time 
  are 
  generally 
  

   spoken 
  of 
  -as 
  pre-Cambric. 
  

  

  The 
  following 
  table 
  embodies 
  the 
  result 
  of 
  the 
  latest 
  studies.^ 
  

   The 
  thicknesses 
  are 
  chiefly 
  obtained 
  from 
  well 
  records 
  published 
  by 
  

   Prof. 
  L 
  P. 
  Bishop. 
  The 
  relations 
  of 
  these 
  strata 
  to 
  each 
  other 
  in 
  

   this 
  region 
  are 
  shown 
  in 
  the 
  north 
  and 
  south 
  section 
  from 
  Canada 
  to 
  

   the 
  New 
  York-Pennsylvania 
  line, 
  presented 
  in 
  fig. 
  i. 
  

  

  Ever 
  since 
  the 
  days 
  of 
  Lyell 
  and 
  Hall 
  the 
  life 
  history 
  of 
  Niagara 
  

   and 
  the 
  origin 
  of 
  the 
  Great 
  lakes 
  has 
  engaged 
  the 
  attention 
  of 
  

   geologists 
  the 
  world 
  over. 
  Among 
  the 
  names 
  prominent 
  in 
  con- 
  

   nection 
  with 
  studies 
  of 
  the 
  geology 
  of 
  Niagara 
  in 
  one 
  or 
  more 
  of 
  

   its 
  aspects, 
  may 
  be 
  mentioned 
  those 
  of 
  Bishop, 
  Clarke, 
  Claypole, 
  

   Davis, 
  Fairchild, 
  Gilbert, 
  Hall, 
  Hitchcock, 
  Lesley, 
  Lyell, 
  Newberry, 
  

   Pohlman, 
  Ringueberg, 
  Shaler, 
  Spencer, 
  Tarr, 
  Taylor, 
  Upham 
  and 
  

   Wright, 
  besides 
  a 
  host 
  of 
  others. 
  ^ 
  

  

  ^Clarke 
  and 
  Schuchert. 
  Science, 
  n. 
  s. 
  Dec. 
  15, 
  1899, 
  10:3. 
  It 
  will 
  be 
  

   found 
  to 
  differ 
  in 
  some 
  respects 
  from 
  the 
  table 
  published 
  in 
  the 
  author's 
  

   Geology 
  of 
  Eighteen 
  Mile 
  creek, 
  etc. 
  

  

  ^In 
  the 
  field 
  work 
  I 
  have 
  had 
  the 
  efficient 
  assistance 
  of 
  my 
  friend 
  Mr 
  R. 
  F. 
  

   Morgan 
  of 
  Buffalo. 
  

  

  