﻿AGE 
  OF 
  THE 
  EARTH 
  — 
  CHAMBERLIN 
  AND 
  OTHERS. 
  245 
  

  

  In 
  considering 
  the 
  standard 
  water-lain 
  sediments 
  of 
  the 
  column, 
  

   it 
  is 
  to 
  be 
  understood 
  that 
  only 
  rapid 
  surveys 
  or 
  mere 
  reconnais- 
  

   sances 
  have 
  as 
  yet 
  been 
  made 
  of 
  the 
  larger 
  part 
  of 
  the 
  earth, 
  and 
  that 
  

   inevitabfy 
  inconspicuous 
  breaks 
  in 
  the 
  continuity 
  of 
  the 
  deposits 
  have 
  

   been 
  overlooked. 
  As 
  a 
  result 
  recent 
  critical 
  studies 
  have 
  revealed 
  in 
  

   some 
  cases 
  surprising 
  numbers 
  of 
  gaps 
  in 
  the 
  continuity 
  of 
  deposi- 
  

   tion. 
  For 
  example, 
  Dr. 
  Stuart 
  Weller, 
  in 
  a 
  study 
  of 
  what 
  was 
  for- 
  

   merly 
  regarded 
  as 
  a 
  continuous 
  section 
  of 
  the 
  Mississippian, 
  has 
  

   found 
  no 
  less 
  than 
  12 
  breaks 
  in 
  continuity. 
  The 
  time 
  value 
  of 
  these, 
  

   in 
  his 
  judgment, 
  is 
  two 
  or 
  three 
  times 
  as 
  great 
  as 
  that 
  of 
  the 
  visible 
  

   beds 
  themselves. 
  8 
  The 
  time 
  values 
  of 
  such 
  intervals 
  are 
  best 
  judged 
  

   by 
  comparing 
  the 
  faunas 
  below 
  them 
  with 
  those 
  above, 
  but 
  this 
  falls 
  

   within 
  the 
  province 
  of 
  my 
  paleontological 
  colleague, 
  and 
  I 
  therefore 
  

   leave 
  this 
  source 
  of 
  correction 
  in 
  his 
  hands, 
  merely 
  expressing 
  the 
  

   conviction 
  that 
  these 
  breaks 
  in 
  the 
  continuity 
  of 
  the 
  sediments 
  are 
  

   quite 
  sure, 
  when 
  finally 
  and 
  fully 
  adjudicated, 
  to 
  extend 
  greatly 
  the 
  

   old 
  estimates 
  of 
  the 
  time 
  occupied 
  in 
  sedimentation. 
  

  

  2. 
  Human 
  acceleration 
  of 
  the 
  rate 
  of 
  deposition. 
  — 
  To 
  pioneers 
  

   who 
  watched 
  the 
  effects 
  of 
  floods, 
  freshets, 
  and 
  ordinary 
  wash 
  on 
  the 
  

   native 
  surface 
  of 
  our 
  prairies 
  and 
  forests 
  in 
  their 
  virgin 
  state, 
  and 
  

   who 
  are 
  able 
  now 
  to 
  compare 
  this 
  with 
  the 
  present 
  wash 
  of 
  the 
  same 
  

   surfaces 
  under 
  cultivation, 
  there 
  is 
  no 
  need 
  to 
  argue 
  that 
  human 
  

   intervention 
  has 
  greatly 
  hastened 
  denudation 
  and 
  deposition. 
  In 
  

   the 
  native 
  state 
  the 
  surface 
  was 
  protected 
  by 
  thick 
  mats 
  of 
  grass, 
  

   leaves, 
  and 
  other 
  vegetable 
  debris 
  ; 
  while 
  the 
  soil 
  was 
  bound 
  together 
  

   by 
  dense 
  entanglements 
  of 
  roots. 
  The 
  waters 
  then 
  ran 
  almost 
  clear 
  

   where 
  now 
  they 
  run 
  mud. 
  9 
  Added 
  to 
  this 
  are 
  the 
  quickened 
  defla- 
  

   tion 
  of 
  winds, 
  the 
  wear 
  of 
  roadways, 
  the 
  effects 
  of 
  quarrying 
  and 
  

   other 
  excavation, 
  as 
  well 
  as 
  the 
  actual 
  carting 
  away 
  of 
  clays, 
  sands, 
  

   gravels, 
  quarry 
  stone, 
  foodstuffs, 
  timber, 
  and 
  other 
  material. 
  While 
  

   it 
  is 
  not 
  easy 
  to 
  fix 
  on 
  a 
  definite 
  measure 
  of 
  these 
  effects, 
  the 
  needed 
  

   correction 
  seems 
  certainly 
  to 
  be 
  large. 
  

  

  3. 
  Correction 
  for 
  the 
  present 
  elevation 
  of 
  the 
  surface. 
  — 
  It 
  is 
  held 
  by 
  

   leading 
  American 
  geologists 
  that 
  the 
  general 
  elevatory 
  movements 
  of 
  

   the 
  continents 
  have 
  alternated 
  with 
  periods 
  of 
  relative 
  stability 
  dur- 
  

   ing 
  which 
  the 
  processes 
  of 
  base 
  leveling 
  and 
  sea 
  transgression 
  have 
  

  

  8 
  Personal 
  communication. 
  

  

  8 
  A 
  fuller 
  statement 
  of 
  this 
  with 
  citations 
  of 
  data 
  from 
  Dole 
  and 
  Stabler 
  and 
  from 
  

   F. 
  W. 
  Clarke 
  Is 
  given 
  in 
  " 
  Diatrophisni 
  and 
  the 
  formative 
  processes, 
  VIII, 
  the 
  quantita- 
  

   tive 
  element 
  in 
  continental 
  growth," 
  T. 
  C. 
  Chamberlin, 
  Jour. 
  Geol., 
  Vol. 
  XXII 
  (1913), 
  

   pp. 
  522-528. 
  

  

  55379—24 
  17 
  

  

  