﻿Appalachian 
  Geosyncline. 
  433 
  

  

  Previous 
  Views 
  Regarding 
  Conditions 
  of 
  Origin. 
  

  

  In 
  order 
  to 
  form 
  a 
  comprehensive 
  background 
  for 
  the 
  dis- 
  

   cussion 
  of 
  these 
  fossil-barren 
  formations 
  of 
  the 
  Upper 
  Devo- 
  

   nian, 
  a 
  review 
  of 
  opinions 
  regarding 
  their 
  conditions 
  of 
  origin, 
  

   which 
  have 
  been 
  expressed 
  during 
  the 
  past 
  twenty 
  years 
  by 
  

   geologists 
  mostly 
  still 
  living, 
  will 
  here 
  be 
  given. 
  The 
  divers- 
  

   ity 
  of 
  these 
  prevailing 
  views 
  demonstrates 
  the 
  room 
  for 
  further 
  

   study. 
  It 
  should 
  be 
  said 
  in 
  explanation, 
  however, 
  that 
  certain 
  

   of 
  the 
  quotations, 
  especially 
  those 
  from 
  manuals, 
  are 
  from 
  

   geologists, 
  who, 
  although 
  authoritative 
  in 
  their 
  fields, 
  either 
  

   may 
  T 
  not 
  profess 
  to 
  have 
  personal 
  knowledge 
  of 
  the 
  formations 
  

   in 
  question, 
  or 
  else 
  were 
  not 
  regarding 
  the 
  problem 
  of 
  origin 
  

   as 
  the 
  principal 
  point 
  in 
  their 
  investigations. 
  Others 
  of 
  the 
  

   opinions 
  were 
  expressed 
  before 
  the 
  importance 
  of 
  subaerial 
  

   delta 
  deposits 
  in 
  sedimentation 
  had 
  become 
  appreciated 
  or 
  their 
  

   criteria 
  recognized 
  and 
  their 
  authors 
  at 
  the 
  present 
  time 
  might 
  

   modify 
  materially 
  their 
  conclusions. 
  Practically 
  no 
  statements 
  

   have 
  appeared, 
  however, 
  in 
  regard 
  to 
  the 
  climatic 
  factors 
  

   which 
  controlled 
  the 
  nature 
  of 
  the 
  deposits, 
  though 
  the 
  present 
  

   writer 
  holds 
  them 
  to 
  be 
  as 
  fundamental 
  as 
  the 
  cooperating 
  

   topographic 
  conditions. 
  

  

  J. 
  J. 
  Stevenson 
  in 
  1891, 
  in 
  his 
  Yice-Presidential 
  address 
  to 
  

   the 
  American 
  Association 
  for 
  the 
  Advancement 
  of 
  Science, 
  

   concluded 
  that 
  the 
  deposits 
  of 
  the 
  Catskill 
  epoch 
  were 
  laid 
  

   down 
  in 
  an 
  open 
  sea, 
  not 
  made 
  in 
  a 
  closed 
  sea 
  or 
  in 
  fresh- 
  

   water 
  lakes, 
  since 
  the 
  strata 
  are 
  continuous 
  from 
  the 
  Catskill 
  

   into 
  the 
  Chemung.* 
  The 
  Catskill 
  and 
  Chemung 
  were 
  laid 
  

   down 
  in 
  a 
  shallow 
  basin 
  subsiding 
  most 
  rapidly 
  at 
  the 
  east 
  with 
  

   deposits 
  much 
  thicker 
  near 
  the 
  mainland. 
  

  

  "The 
  molluscan 
  fauna 
  of 
  the 
  Chemung 
  and 
  Catskill 
  is 
  unques- 
  

   tionably 
  marine. 
  Even 
  the 
  mollusks 
  found 
  in 
  New 
  York 
  above 
  

   the 
  Oneonta 
  sandstone 
  belong 
  to 
  the 
  ordinary 
  forms. 
  Of 
  course 
  

   it 
  is 
  possible, 
  even 
  probable, 
  that 
  at 
  the 
  extreme 
  northeast 
  there 
  

   were 
  small 
  areas 
  at 
  the 
  mouths 
  of 
  large 
  rivers 
  where 
  fresh 
  water 
  

   prevailed 
  and 
  fresh-water 
  mollusks 
  lived 
  ; 
  but 
  positive 
  evidence 
  

   of 
  this 
  is 
  wanting. 
  The 
  Amphigenia 
  found 
  in 
  the 
  Oneonta 
  sand- 
  

   stone 
  of 
  New 
  York 
  may 
  be 
  a 
  fresh-water 
  form, 
  but 
  it 
  occurs 
  in 
  

   the 
  Montrose 
  sandstone 
  in 
  southern 
  Pennsylvania 
  so 
  far 
  away 
  

   from 
  the 
  old 
  shore 
  line 
  that 
  fresh-water 
  conditions 
  seem 
  certainly 
  

   improbable." 
  (Stevenson, 
  loc. 
  cit., 
  p. 
  242.) 
  

  

  But 
  the 
  change 
  of 
  view 
  in 
  regard 
  to 
  the 
  conditions 
  of 
  origin 
  

   of 
  many 
  formations 
  is 
  well 
  illustrated 
  by 
  Stevenson's 
  thorough 
  

   studies 
  on 
  the 
  " 
  Formation 
  of 
  Coal 
  Beds,"f 
  where 
  he 
  states, 
  in 
  

  

  * 
  The 
  Chemung 
  and 
  Catskill 
  (Upper 
  Devonian) 
  on 
  the 
  eastern 
  side 
  of 
  the 
  

   Appalachian 
  Basin. 
  Proc. 
  Am. 
  Assoc. 
  Adv. 
  Sci., 
  xl, 
  1891, 
  pp. 
  242-247. 
  

   fSee 
  particularly 
  Proc. 
  American 
  Phil. 
  Soc, 
  vol. 
  li, 
  pp. 
  243-373, 
  1912. 
  

  

  