﻿274 
  G. 
  R. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  Firstly, 
  Cordaites 
  which 
  still 
  held 
  a 
  fast 
  lessening 
  place 
  in 
  the 
  

   early 
  Jura 
  leaves 
  behind 
  only 
  a 
  few 
  lingering 
  hypothetical 
  forms 
  

   like 
  Eolirion. 
  

  

  Secondly 
  ', 
  the 
  Equisetums 
  left 
  over 
  in 
  the 
  Jura-Rhaetic 
  groups 
  

   are 
  now 
  positively 
  reduced 
  to 
  present 
  day 
  scant 
  numbers. 
  

  

  Thirdly, 
  the 
  high 
  frequency 
  of 
  ferns 
  represents 
  the 
  culmina- 
  

   tion 
  of 
  the 
  mid-Mesozoic 
  fern 
  recrudescence 
  due 
  to 
  the 
  spread 
  of 
  

   the 
  more 
  strictly 
  modern 
  types, 
  as 
  mentioned 
  further 
  on. 
  

  

  Fourthly, 
  the 
  persistent 
  presence 
  of 
  conifers 
  in 
  numbers 
  at 
  first 
  

   sharply 
  increasing 
  and 
  then 
  followed 
  by 
  decline 
  in 
  both 
  the 
  per- 
  

   centage 
  and 
  actual 
  number 
  of 
  species 
  recovered, 
  is 
  in 
  striking 
  

   contrast 
  to 
  the 
  moderate 
  numbers 
  of 
  the 
  lower 
  Jura. 
  It 
  ma}^ 
  in 
  

   fact, 
  be 
  definitely 
  accepted 
  that, 
  taking 
  the 
  world 
  over, 
  a 
  strong 
  

   fifth 
  of 
  lower 
  Cretaceous 
  vegetation 
  was 
  coniferous. 
  This 
  is 
  the 
  

   proportion 
  in 
  the 
  English 
  Wealden, 
  in 
  the 
  Potomac, 
  and 
  appar- 
  

   ently 
  in 
  all 
  the 
  horizons 
  where 
  collecting 
  has 
  been 
  most 
  thorough. 
  

   The 
  44 
  per 
  cent 
  of 
  the 
  Portuguese 
  Aptian 
  and 
  7 
  per 
  cent 
  of 
  the 
  

   Japanese 
  Neocomian 
  balance 
  each 
  other 
  as 
  abnormal 
  proportions 
  

   unquestionably 
  due 
  to 
  lack 
  of 
  fortune 
  afield. 
  In 
  a 
  word, 
  just 
  as 
  

   the 
  early 
  Jura 
  was 
  a 
  period 
  of 
  vast 
  reaches 
  of 
  VVilliamsonians, 
  so 
  

   quite 
  all 
  the 
  Lower 
  Cretaceous 
  was 
  the 
  time 
  of 
  dominant 
  conifer- 
  

   ous 
  forests 
  which 
  receded 
  with 
  the 
  advance 
  of 
  the 
  angiosperms. 
  

  

  Fifthly, 
  the 
  cycadophytan 
  and 
  coniferous 
  elements 
  quite 
  

   exactly 
  balance 
  each 
  other, 
  the 
  time 
  when 
  these 
  gymnospermous 
  

   types 
  are 
  to 
  reverse 
  their 
  Jurassic 
  proportions 
  being 
  near 
  at 
  

   hand.* 
  

  

  The 
  preparation 
  of 
  Table 
  II 
  at 
  once 
  showed 
  that 
  the 
  lower 
  

   half 
  of 
  the 
  Consuelo 
  plant 
  beds 
  contains 
  elements 
  which 
  any 
  

   paleobotanist 
  would, 
  as 
  already 
  insisted 
  upon, 
  recognize 
  as 
  

   belonging 
  to 
  , 
  a 
  slightly 
  older 
  facies 
  than 
  the 
  plants 
  of 
  the 
  

   upper 
  half. 
  That 
  is 
  to 
  say, 
  even 
  were 
  these 
  two 
  series 
  of 
  

   plants 
  obtained 
  in 
  widely 
  separated 
  regions, 
  the 
  fact 
  that 
  they 
  

   bear 
  a 
  successional 
  rather 
  than 
  an 
  equivalent 
  relation 
  would 
  be 
  

   evident. 
  Nevertheless, 
  the 
  difference 
  is, 
  in 
  the 
  present 
  state 
  

   of 
  our 
  knowledge 
  of 
  Lower 
  Jurassic 
  florge, 
  not 
  strongly 
  enough 
  

   pronounced 
  to 
  permit 
  more 
  than 
  fairly 
  taken 
  surmises. 
  Especi- 
  

  

  * 
  Where 
  these 
  florae 
  do 
  vary 
  markedly 
  from 
  the 
  expected 
  or 
  average 
  type, 
  

   restudy 
  in 
  both 
  laboratory 
  and 
  field 
  is 
  urgent. 
  Take 
  for 
  instance 
  the 
  Urgo- 
  

   nian 
  of 
  Austria 
  -Hungary. 
  If 
  the 
  commonly 
  found 
  ferns 
  and 
  conifers 
  of 
  

   Urgonian 
  time 
  were 
  arbitrarily 
  added 
  to 
  that 
  list, 
  the 
  normal 
  proportion 
  of 
  

   about 
  45 
  per 
  cent 
  ferns, 
  20 
  per 
  cent 
  cycads 
  and 
  25 
  per 
  cent 
  conifers 
  would 
  

   at 
  once 
  be 
  had, 
  and 
  the 
  presumption 
  is 
  strong 
  that 
  either 
  additional 
  ferns 
  

   can 
  be 
  found 
  in 
  the 
  formations 
  in 
  question, 
  or 
  else 
  we 
  must 
  take 
  the 
  only 
  

   remaining 
  alternative 
  view 
  that 
  the 
  series 
  is 
  of 
  somewhat 
  aberrant 
  early 
  

   Wealden 
  type. 
  

  

  , 
  Similarly 
  in 
  the 
  Wealden 
  of 
  Germany 
  we 
  may 
  arbitrarily 
  declare 
  that 
  the 
  

   reverse 
  holds, 
  cycad 
  and 
  conifer 
  collection 
  and 
  determination 
  having 
  failed 
  

   to 
  keep 
  pace 
  with 
  fern 
  recovery. 
  At 
  least 
  the 
  cases 
  cited 
  offset 
  each 
  other 
  

   and 
  the 
  burden 
  of 
  proof 
  must 
  primarily 
  rest 
  on 
  any 
  explanation 
  invoking 
  

   changed 
  local 
  conditions, 
  sufficient 
  to 
  account 
  for 
  such 
  deep-seated 
  varia- 
  

   tions 
  as 
  would 
  be 
  indicated 
  were 
  some 
  of 
  the 
  German 
  Wealden 
  proportions 
  

   found 
  approximately 
  true 
  ones. 
  

  

  