﻿Appalachian 
  Geosyncline. 
  431 
  

  

  tions. 
  These 
  rocks 
  are 
  almost 
  barren 
  of 
  fossils 
  and 
  those 
  

   which 
  do 
  occur 
  are 
  fragmentary 
  impressions 
  of 
  plants 
  and 
  

   scanty 
  traces 
  of 
  animal 
  life, 
  none 
  of 
  which 
  is 
  declaredly 
  marine. 
  

   These 
  barren 
  formations 
  stand 
  in 
  contrast 
  to 
  the 
  fossiliferous 
  

   dark 
  gray 
  or 
  green 
  Portage 
  and 
  Chemung 
  shales 
  and 
  sandstones 
  

   which 
  represent 
  the 
  same 
  epochs 
  of 
  geologic 
  time 
  farther 
  to 
  

   the 
  west 
  and 
  south. 
  The 
  chronologic 
  relations 
  of 
  the 
  forma- 
  

   tions 
  of 
  the 
  two 
  regions 
  to 
  each 
  other 
  was 
  for 
  a 
  time 
  the 
  chief 
  

   problem, 
  but 
  that 
  gradually 
  became 
  understood 
  and 
  the 
  equiva- 
  

   lences 
  of 
  the 
  Oneonta 
  to 
  the 
  Portage 
  beds, 
  the 
  Catskill 
  to 
  the 
  

   Chemung, 
  are 
  now 
  universally 
  accepted. 
  

  

  But 
  under 
  what 
  physical, 
  and 
  climatic 
  conditions 
  were 
  these 
  

   several 
  formations 
  laid 
  down 
  1 
  Why 
  are 
  the 
  eastern 
  forma- 
  

   tions 
  different 
  from 
  the 
  synchronous 
  sands 
  and 
  clays 
  deposited 
  

   farther 
  west 
  ? 
  What 
  causes 
  excluded 
  the 
  preservation 
  of 
  fos- 
  

   sils 
  ? 
  These 
  are 
  questions 
  to 
  which 
  no 
  unanimity 
  of 
  answers 
  

   has 
  been 
  given. 
  Even 
  those 
  which 
  have 
  been 
  advanced 
  may 
  

   be 
  characterized, 
  in 
  most 
  cases, 
  as 
  opinions 
  incidental 
  to 
  geo- 
  

   logic 
  descriptions 
  rather 
  than 
  attempts 
  at 
  demonstration. 
  The 
  

   earlier 
  conclusions 
  furthermore 
  have 
  rested 
  upon 
  premises 
  

   regarding 
  the 
  processes 
  of 
  sedimentation 
  which 
  in 
  themselves 
  

   in 
  some 
  respects 
  have 
  either 
  not 
  been 
  sound 
  or 
  not 
  conclu- 
  

   sively 
  demonstrated. 
  In 
  an 
  earlier 
  decade 
  the 
  simple 
  dictum 
  

   prevailed 
  that 
  sediments 
  in 
  general 
  were 
  deposited 
  in 
  permanent 
  

   bodies 
  of 
  water, 
  — 
  marine, 
  estuarine, 
  or 
  lacustrine, 
  according 
  to 
  

   the 
  indications 
  of 
  the 
  fossils. 
  But 
  a 
  wider 
  study 
  of 
  the 
  earth 
  

   has 
  shown 
  the 
  large 
  importance 
  of 
  terrestrial 
  deposition 
  and 
  

   the 
  view 
  that 
  the 
  eastern 
  formations 
  of 
  the 
  Upper 
  Devonian 
  

   are 
  subaerial 
  delta 
  deposits, 
  entirely 
  removed 
  from 
  the 
  sea 
  or 
  

   bodies 
  of 
  permanent 
  water, 
  would 
  not 
  at 
  present 
  appear 
  radi- 
  

   cal. 
  Yet 
  this 
  is 
  contrary 
  to 
  most 
  of 
  the 
  opinions 
  which 
  have 
  

   been 
  published 
  during 
  the 
  past 
  twenty 
  years. 
  Furthermore, 
  

   to 
  obtain 
  scientific 
  standing 
  such 
  a 
  contention 
  must 
  rest 
  upon 
  

   a 
  basis 
  of 
  demonstration; 
  not 
  merely 
  upon 
  a 
  present 
  apprecia- 
  

   tion 
  of 
  the 
  larger 
  importance 
  of 
  alluvial 
  deposition 
  ; 
  else 
  in, 
  

   another 
  decade 
  the 
  pendulum 
  of 
  opinion 
  may 
  swing 
  backward 
  

   and 
  carry 
  away 
  from 
  under 
  it 
  the 
  basis 
  for 
  such 
  a 
  conclusion. 
  

  

  The 
  Oneonta 
  and 
  Catskill 
  formations 
  rarely 
  exhibit 
  those 
  

   obvious 
  and 
  positive 
  evidences 
  which 
  make 
  the 
  demonstration 
  

   of 
  the 
  conditions 
  of 
  origin 
  of 
  certain 
  other 
  formations 
  rela- 
  

   tively 
  easy 
  and 
  sure. 
  During 
  a 
  period 
  of 
  eight 
  years 
  the 
  

   writer 
  has, 
  however, 
  studied 
  these 
  formations 
  in 
  the 
  field 
  as 
  

   opportunities 
  arose, 
  examining 
  sections 
  between 
  the 
  Hudson 
  

   and 
  Potomac 
  rivers. 
  The 
  results 
  of 
  those 
  studies, 
  resting 
  in 
  

   turn 
  upon 
  other 
  studies 
  on 
  the 
  nature 
  of 
  sedimentation, 
  are 
  

   embodied 
  in 
  this 
  article 
  and 
  the 
  conclusions 
  are 
  here 
  reached 
  

   that 
  these 
  Upper 
  Devonian 
  formations 
  represent 
  subaerial 
  delta 
  

   deposits 
  in 
  a 
  dry 
  but 
  not 
  arid 
  climate 
  ; 
  a 
  climate 
  probably 
  

  

  