﻿G. 
  R. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  273 
  

  

  trate 
  both 
  the 
  advantages 
  and 
  the 
  limits 
  of 
  the 
  method 
  pursued 
  

   in 
  determining 
  the 
  age 
  of 
  the 
  Oaxacan 
  plants, 
  it 
  will 
  not 
  be 
  

   found 
  amiss 
  to 
  take 
  a 
  hasty 
  glance 
  at 
  plant 
  proportions 
  in 
  the 
  

   Lower 
  Cretaceous 
  — 
  a 
  rapid 
  survey 
  which 
  has 
  been 
  rendered 
  

   easy 
  by 
  Berry's 
  recent 
  resume 
  of 
  the 
  Lower 
  Cretaceous 
  floras 
  

   of 
  the 
  world. 
  

  

  This 
  more 
  distant 
  comparison 
  with 
  the 
  Lower 
  Cretaceous 
  is 
  

   not 
  without 
  tangible 
  interest 
  and 
  may 
  be 
  given 
  a 
  concise 
  

   enough 
  form 
  for 
  interpolation. 
  For 
  this 
  purpose 
  Table 
  Ya 
  

   has 
  been 
  prepared 
  to 
  show 
  the 
  main 
  elements 
  of 
  twelve 
  of 
  the 
  

   more 
  striking 
  Lower 
  Cretaceous 
  floras. 
  

  

  Table 
  Ya. 
  — 
  Twelve 
  Lower 
  Cretaceous 
  Floras. 
  

  

  %'* 
  

  

  i 
  

  

  •-3 
  

  

  1 
  

  

  3 
  

   o 
  

   o 
  

   

  

  d 
  

  

  > 
  

  

  X 
  

  

  c 
  

   B 
  

  

  M 
  

  

  8 
  

  

  Ph 
  

   Ph 
  

  

  CD 
  a 
  

  

  CD 
  

   <D 
  B 
  

  

  1p 
  

  

  d 
  

  

  B 
  

  

  -1-3 
  

  

  o 
  

   o 
  

  

  ~B 
  

   B 
  « 
  

  

  45 
  s 
  

  

  «0 
  

  

  3 
  

   o 
  ,_; 
  

  

  & 
  «s 
  

  

  « 
  p 
  

   cd 
  ■£ 
  

  

  °Ph 
  

  

  d 
  

  

  o3 
  

  

  o 
  

  

  'S 
  

  

  m 
  

   P 
  

  

  B 
  o3 
  

   03 
  fco 
  

  

  o 
  B 
  

  

  O 
  

  

  03 
  

   &D 
  

  

  P 
  

  

  ■43 
  

  

  o 
  

   Ph 
  

  

  a 
  

  

  .2 
  

  

  +=> 
  

  

  03 
  

  

  bjc 
  

   P 
  

  

  o 
  

   Ph 
  

  

  B~ 
  

   .2 
  

   3 
  

  

  CO 
  

  

  

  43 
  

  

  P 
  

  

  38 
  

  

  37 
  

  

  38 
  

  

  M 
  

   40 
  

  

  54 
  

  

  47 
  

  

  32 
  

  

  P 
  

  

  17 
  

  

  M 
  

   45 
  

  

  28 
  

  

  3 
  

  

  ^ 
  

  

  Ferns 
  

  

  30 
  

  

  40- 
  

  

  Cycadeans 
  — 
  

  

  47 
  

  

  38 
  

  

  35 
  

  

  33 
  

  

  21 
  

  

  18 
  

  

  10 
  

  

  25 
  

  

  38 
  

  

  12 
  

  

  8 
  

  

  9 
  

  

  23- 
  

  

  Conifers. 
  .... 
  

  

  7 
  

  

  11 
  

  

  11 
  

  

  28 
  

  

  28 
  

  

  21 
  

  

  21 
  

  

  22 
  

  

  17 
  

  

  20 
  

  

  44 
  

  

  18 
  

  

  22. 
  

  

  Angiosperrns. 
  

  

  

  (?) 
  

  

  

  

  

  

  

  17 
  

  

  o 
  

  

  10 
  + 
  

  

  12(1) 
  

  

  32 
  

  

  14-4 
  

  

  No. 
  of 
  species 
  

  

  28 
  

  

  36 
  

  

  70 
  

  

  21 
  

  

  88 
  

  

  33 
  

  

  95 
  

  

  134 
  

  

  29 
  

  

  75 
  

  

  23 
  

  

  66 
  

  

  

  Naturally 
  there 
  are 
  sharp 
  limits 
  to 
  accuracy 
  in 
  so 
  compacted 
  

   a 
  form 
  of 
  presentation. 
  And, 
  of 
  course, 
  the 
  defectiveness 
  of 
  

   the 
  plant 
  record 
  is 
  much 
  accentuated 
  by 
  the 
  small 
  size 
  and 
  

   obvious 
  aberrancy 
  of 
  several 
  of 
  the 
  floras 
  more 
  Or 
  less 
  arbi- 
  

   trarily 
  included. 
  Indeed, 
  at 
  first 
  sight 
  such 
  a 
  table 
  appears 
  to 
  

   have 
  a 
  rather 
  minor 
  value, 
  and 
  one 
  is 
  mainly 
  aware 
  that 
  no 
  

   one 
  has 
  ventured 
  to 
  present 
  it 
  hitherto 
  ; 
  while 
  every 
  paleon- 
  

   tologist 
  knows 
  well 
  that 
  these 
  general 
  percentages 
  may 
  even 
  

   be 
  as 
  little 
  accurate 
  for 
  the 
  floras 
  actually 
  recoverable 
  in 
  a 
  

   given 
  region, 
  as 
  representative 
  of 
  the 
  ancient 
  plant 
  proportions. 
  

  

  Nevertheless, 
  there 
  is 
  more 
  than 
  a 
  mere 
  assumption 
  that 
  the 
  

   inaccuracies 
  so 
  obviously 
  and 
  inherently 
  involved 
  in 
  no 
  incon- 
  

   siderable 
  degree 
  balance 
  each 
  other. 
  For 
  neither 
  the 
  exigen- 
  

   cies 
  of 
  fossilization, 
  nor 
  climatic 
  variation, 
  nor 
  yet 
  the 
  varying 
  

   personal 
  equation 
  involved 
  in 
  the 
  determination 
  of 
  these 
  frag- 
  

   mentary 
  records 
  from 
  many 
  lands, 
  can 
  wholly 
  obscure 
  the 
  larger 
  

   outlines 
  of 
  Cretaceous 
  vegetation. 
  Generally 
  consistent 
  and 
  

   inescapably 
  salient 
  are 
  the 
  following 
  features 
  : 
  

  

  