﻿268 
  

  

  G. 
  B. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  that 
  these 
  plants 
  culminate 
  in 
  numbers 
  low 
  down 
  in 
  the 
  Seccion 
  

   Consuelo, 
  which 
  is 
  below 
  shown 
  to 
  be 
  typical 
  Liassic, 
  proves 
  

   that, 
  — 
  wherever 
  we 
  find 
  beds 
  yielding 
  60 
  per 
  cent 
  or 
  more 
  of 
  

   cycadophytans 
  in 
  fairly 
  representative 
  collections, 
  vie 
  may 
  

   confidently 
  assign 
  them 
  to 
  the 
  very 
  earliest 
  Lias. 
  

  

  I 
  have 
  already 
  pointed 
  out 
  in 
  my 
  recent 
  paper 
  on 
  the 
  Wil- 
  

   liamsonian 
  Tribe 
  that 
  the 
  Cycadophytan 
  genera 
  culminated 
  in 
  

   the 
  Lias, 
  and 
  it 
  may 
  now 
  be 
  regarded 
  as 
  clearly 
  established 
  

   that 
  the 
  beginning 
  of 
  that 
  period 
  witnessed 
  the 
  maximum 
  

   development 
  of 
  cycadeous 
  plants 
  in 
  both 
  variety 
  and 
  actual 
  

   numbers. 
  

  

  A 
  further 
  thought 
  also 
  comes 
  to 
  mind. 
  While 
  it 
  is 
  fortunate 
  

   that 
  we 
  can 
  here 
  deal 
  with 
  an 
  actual 
  plant 
  succession 
  on 
  a 
  large 
  

   scale, 
  and 
  while 
  it 
  is 
  true 
  that 
  the 
  species 
  of 
  the 
  upper 
  half 
  of 
  

   the 
  beds 
  do 
  not 
  vary 
  greatly 
  in 
  general 
  type 
  from 
  those 
  of 
  the 
  

   lower, 
  it 
  is 
  none 
  the 
  less 
  reassuring 
  to 
  find 
  that 
  were 
  the 
  two 
  

   series 
  found 
  far 
  separated, 
  most 
  paleophytologists 
  would, 
  with 
  

   little 
  doubt, 
  reach 
  a 
  fairly 
  correct 
  deduction 
  as 
  to 
  the 
  true 
  

   relative 
  age. 
  The 
  presence 
  of 
  iV 
  oeggerathiopsis 
  in 
  at 
  least 
  two 
  

   distinct 
  leaf 
  species 
  would 
  in 
  itself 
  have 
  some 
  weight 
  in 
  favor 
  

   of 
  the 
  greater 
  age 
  of 
  the 
  plants 
  of 
  the 
  lower 
  beds, 
  while 
  the 
  

   rather 
  older 
  appearance 
  of 
  the 
  accompanying 
  ferns 
  would 
  

   scarcely 
  be 
  overlooked. 
  And 
  that 
  such 
  observations 
  should 
  

   have 
  some 
  value 
  in 
  aiding 
  us 
  to 
  adjudge 
  remotely 
  separated 
  

   geologic 
  sections 
  is 
  fair 
  to 
  emphasize. 
  

  

  Accordingly, 
  the 
  more 
  general 
  group 
  proportions 
  of 
  the 
  

   plants 
  of 
  the 
  lower 
  and 
  upper 
  half 
  of 
  the 
  section 
  are 
  further 
  

   compared 
  by 
  percentages 
  in 
  Table 
  III. 
  And 
  following 
  this 
  

   suggestive 
  table 
  a 
  similar 
  comparison 
  with 
  more 
  widely 
  sepa- 
  

   rated 
  florse, 
  interesting 
  because 
  of 
  similar 
  age 
  or 
  because 
  of 
  

   geographic 
  position, 
  becomes 
  instructive. 
  

  

  Table 
  III. 
  — 
  Plant 
  Grouping 
  in 
  the 
  Rio 
  Consuelo 
  Section. 
  

  

  %'s 
  

  

  Species 
  in 
  the 
  

  

  lower 
  

  

  250 
  meters 
  

  

  Species 
  in 
  the 
  

  

  upper 
  

  

  300 
  meters 
  

  

  Entire 
  section 
  

  

  by 
  

  

  direct 
  count 
  

  

  Cycads 
  

  

  Ferns 
  .. 
  

  

  (]8)+ 
  = 
  72 
  

   (3)+ 
  = 
  12 
  

   3+ 
  = 
  12 
  + 
  

   1 
  = 
  4 
  

   (1) 
  

   25 
  + 
  

  

  (20) 
  = 
  66 
  

   (7) 
  = 
  23 
  

   (?) 
  

  

  (1) 
  = 
  3 
  

   30 
  + 
  

  

  70 
  

  

  18 
  

  

  Cordaites 
  _ 
  . 
  , 
  

  

  Conifers 
  

  

  Equisetums 
  

  

  Total 
  species 
  . 
  . 
  

  

  [8] 
  

  

  2 
  

   , 
  2 
  

  

  