﻿470 
  J. 
  Barrett 
  — 
  Ujpjper 
  Devonian 
  Delta 
  of 
  the 
  

  

  plant 
  types 
  over 
  wide 
  ranges 
  of 
  latitude 
  and 
  longitude. 
  The 
  

   intermediate 
  character 
  of 
  the 
  climate 
  in 
  regard 
  to 
  rainfall 
  is 
  

   indicated 
  by 
  the 
  almost 
  universal 
  absence 
  of 
  either 
  carbon 
  or 
  

   evaporation 
  deposits. 
  Hence 
  there 
  was 
  sufficient 
  dryness 
  and 
  

   oxidation 
  to 
  destroy 
  such 
  organic 
  matter 
  as 
  developed 
  over 
  the 
  

   river 
  flood 
  plains, 
  but 
  sufficient 
  rainfall 
  in 
  excess 
  of 
  evapora- 
  

   tion 
  to 
  prevent 
  in 
  the 
  marginal 
  lagoons 
  the 
  concentration 
  of 
  

   evaporation 
  products. 
  With 
  equable 
  rainfall, 
  throughout 
  the 
  

   year 
  this 
  balance 
  would 
  be 
  more 
  delicate 
  to 
  maintain 
  ; 
  but 
  with 
  

   seasonal 
  rainfall 
  and 
  dryness, 
  the 
  typical 
  climate 
  of 
  the 
  present 
  

   tropics, 
  a 
  wide 
  range 
  may 
  exist 
  in 
  the 
  relative 
  length 
  of 
  the 
  

   seasons 
  and 
  amount 
  of 
  rainfall 
  and 
  still 
  permit 
  the 
  drying 
  of 
  

   the 
  soil 
  at 
  one 
  season, 
  the 
  washing 
  out 
  of 
  evaporation 
  deposits 
  

   at 
  another. 
  

  

  The 
  climate 
  of 
  the 
  Catskill 
  delta 
  has 
  thus 
  been 
  narrowed 
  

   down 
  to 
  two 
  types. 
  First, 
  semi-aridity, 
  characterized 
  by 
  a 
  

   scanty 
  rainfall 
  throughout 
  the 
  year, 
  preventing 
  the 
  luxuriant 
  

   growth 
  of 
  vegetation 
  at 
  any 
  time 
  ; 
  or, 
  second 
  and 
  more 
  probable, 
  

   a 
  climate 
  of 
  seasonal 
  rainfall, 
  probably 
  in 
  the 
  growing 
  

   season, 
  since 
  this 
  favors 
  herbaceous 
  rather 
  than 
  arboreal 
  

   vegetation. 
  Semi-aridity 
  gives 
  rise 
  to 
  the 
  pampas 
  of 
  Argentina 
  

   and 
  the 
  staked 
  plains 
  of 
  Texas 
  ; 
  abundant 
  but 
  seasonal 
  rainfall 
  

   to 
  the 
  llano 
  of 
  the 
  Orinoco, 
  the 
  savannas 
  of 
  tropical 
  Africa 
  

   and 
  the 
  monsoon 
  tracts 
  in 
  India. 
  A 
  rather 
  warm 
  climate 
  is 
  

   suggested, 
  since 
  such 
  favors 
  rapid 
  drying 
  and 
  oxidation 
  of 
  the 
  

   soil. 
  

  

  The 
  climatic 
  conditions 
  which 
  have 
  been 
  inferred 
  stand 
  

   between 
  those 
  which 
  gave 
  rise 
  to 
  the 
  carbonaceous 
  muds 
  and 
  

   dark 
  sands 
  of 
  the 
  Middle 
  Devonian, 
  even 
  where 
  these 
  hold 
  

   terrestrial 
  deposits 
  as 
  in 
  the 
  Bellvale 
  flags 
  ; 
  and 
  the 
  red 
  sand- 
  

   stones 
  of 
  the 
  upper 
  Mississippian 
  with 
  the 
  gypsum 
  deposits 
  of 
  

   Nova 
  Scotia 
  and 
  Virginia, 
  and 
  the 
  briny 
  strata 
  of 
  Michigan. 
  

   The 
  climatic 
  movement 
  at 
  the 
  close 
  of 
  the 
  Middle 
  Devonian 
  

   was 
  not 
  severe, 
  but 
  was 
  sufficient 
  to 
  result 
  in 
  effective 
  oxidation 
  

   of 
  alluvial 
  muds 
  where 
  previously 
  this 
  had 
  not 
  taken 
  place. 
  

   With 
  the 
  beginning 
  of 
  the 
  Mississippian 
  a 
  greater 
  climatic 
  

   instability 
  manifested 
  itself, 
  conditions 
  favorable 
  to 
  the 
  

   development 
  of 
  coal 
  marking 
  the 
  early 
  Mississippian, 
  but 
  not 
  

   unmixed 
  with 
  evidences 
  of 
  oxidation 
  and 
  evaporation 
  occasion- 
  

   ally 
  more 
  pronounced 
  than 
  in 
  Devonian 
  times. 
  Finally, 
  in 
  later 
  

   Mississippian 
  times, 
  a 
  period 
  of 
  considerable 
  aridity 
  set 
  in. 
  

   , 
  Having 
  made 
  this 
  analysis 
  of 
  climatic 
  conditions 
  from 
  the 
  

   physical 
  and 
  chemical 
  characteristics 
  of 
  the 
  strata, 
  it 
  is 
  of 
  

   interest 
  to 
  note 
  the 
  conclusions 
  which 
  have 
  been 
  derived 
  regard- 
  

   ing 
  Upper 
  Devonian 
  climates 
  by 
  the 
  students 
  of 
  fossil 
  vegetation. 
  

  

  In 
  a 
  study 
  of 
  the 
  upper 
  Paleozoic 
  floras, 
  their 
  succession 
  and 
  

   range, 
  David 
  White 
  states 
  

  

  