﻿256 
  G. 
  R. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  at 
  some 
  length 
  in 
  my 
  above 
  mentioned 
  first 
  contribution 
  on 
  

   the 
  Williamsonias 
  of 
  the 
  Mixteca 
  Alta 
  ; 
  though 
  unhappily 
  the 
  

   revolutions 
  of 
  the 
  past 
  few 
  years 
  have 
  rendered 
  exploration 
  

   unsafe, 
  and 
  thus 
  far 
  prevented 
  a 
  resumption 
  of 
  the 
  work 
  I 
  

   much 
  wished 
  to 
  make. 
  

  

  Moreover, 
  it 
  should 
  be 
  especially 
  emphasized 
  that 
  the 
  Liassic 
  

   plant 
  beds 
  form 
  only 
  about 
  a 
  third 
  of 
  the 
  entire 
  thickness 
  of 
  

   freshwater 
  and 
  marine 
  Mesozoic 
  so 
  sharply 
  cut 
  through 
  on 
  the 
  

   Barranca 
  Consuelo. 
  The 
  superposed 
  Jurassic 
  and 
  Cretaceous 
  

   strata 
  aggregating 
  a 
  mile 
  in 
  thickness 
  may 
  also 
  be 
  measured 
  

   with 
  an 
  approach 
  to 
  the 
  accuracy 
  permitted 
  by 
  the 
  exposures 
  in 
  a 
  

   quarry. 
  Omitting 
  however 
  any 
  measurements 
  of 
  superposed 
  

   beds, 
  we 
  may 
  now 
  give 
  the 
  preliminary 
  measurements 
  of 
  the 
  

   plant 
  beds 
  with 
  brief 
  field 
  notes. 
  Though 
  I 
  should 
  add 
  that 
  the 
  

   full 
  Mesozoic 
  section 
  of 
  the 
  Barranca 
  Consuelo 
  series 
  was 
  subse- 
  

   quently 
  remeasured 
  conjointly 
  with 
  SenorBonillas, 
  then 
  engaged 
  

   in 
  geologic 
  mapping 
  of 
  the 
  Tezoatlan-Tlaxiaco 
  region, 
  the 
  utmost 
  

   care 
  being 
  taken 
  to 
  not 
  only 
  make 
  all 
  measurements 
  exact, 
  but 
  

   bring 
  the 
  elements 
  of 
  the 
  section 
  into 
  briefer 
  form 
  for 
  carto- 
  

   graphic 
  purposes. 
  The 
  second 
  measurements 
  in 
  actuality 
  vary 
  

   but 
  little 
  from 
  those 
  which 
  here 
  follow 
  as 
  being 
  of 
  the 
  greater 
  

   present 
  interest 
  because 
  made 
  from 
  the 
  immediate 
  viewpoint 
  

   of 
  the 
  collector 
  of 
  fossil 
  plants. 
  But 
  the 
  plant 
  beds 
  are 
  the 
  

   only 
  portion 
  of 
  the 
  Consuelo 
  section 
  with 
  which 
  it 
  is 
  practical 
  

   to 
  now 
  concern 
  ourselves. 
  Furthermore 
  the 
  extended 
  section 
  

   is 
  given 
  in 
  the 
  completed 
  memoir. 
  

  

  Given 
  just 
  as 
  jotted 
  down 
  in 
  the 
  field 
  the 
  measurements 
  which 
  

   follow 
  must 
  prove 
  an 
  aid 
  to 
  future 
  collectors 
  who 
  will 
  not 
  fail 
  to 
  

   revisit 
  and 
  restudy 
  this 
  most 
  important 
  type 
  section 
  for 
  the 
  North 
  

   American 
  Lias. 
  For 
  I 
  urge 
  alike 
  the 
  necessity 
  of 
  keeping 
  the 
  

   records 
  of 
  subsequent 
  collections 
  clear, 
  and 
  the 
  richness 
  and 
  

   promise 
  of 
  this 
  great 
  section. 
  To 
  an 
  inexperienced 
  collector 
  it 
  

   might 
  appear 
  barren, 
  though 
  after 
  patient 
  examination 
  the 
  rich- 
  

   ness 
  of 
  the 
  record 
  conserved 
  will 
  never 
  fail 
  to 
  excite 
  even 
  wonder. 
  

   How 
  the 
  great 
  collections 
  here 
  certain 
  to 
  be 
  made 
  will 
  finally 
  

   appear 
  no 
  one 
  may 
  venture 
  to 
  guess 
  ; 
  though 
  many 
  questions 
  

   already 
  rise 
  to 
  mind. 
  To 
  say 
  nothing 
  of 
  the 
  absence 
  of 
  the 
  

   conifers 
  so 
  far, 
  it 
  is 
  for 
  instance 
  even 
  more 
  singular 
  that 
  of 
  all 
  

   that 
  remarkable 
  group 
  of 
  net-veined 
  lyre-ferns 
  of 
  the 
  Dictyophyl- 
  

   lum- 
  Clathropteris 
  series 
  so 
  strongly 
  characterizing 
  the 
  Khatic 
  of 
  

   Tonkin, 
  and 
  still 
  in 
  part 
  persistent 
  in 
  the 
  European 
  Jura, 
  not 
  a 
  

   trace 
  has 
  yet 
  been 
  found 
  here. 
  Bar 
  contrary 
  testimony 
  from 
  the 
  

   field 
  the 
  explanation 
  nearest 
  at 
  hand 
  is 
  of 
  course 
  that 
  the 
  Tonkin 
  

   flora 
  not 
  only 
  marks 
  a 
  time 
  of 
  dominance 
  for 
  these 
  net-veined 
  

   types 
  of 
  pre- 
  Any 
  io 
  sperm 
  time 
  but 
  that 
  they 
  indicate 
  a 
  tropic 
  

   climate 
  more 
  constantly 
  moist 
  than 
  was 
  that 
  of 
  the 
  Oaxacan 
  Lias, 
  

   which 
  was 
  probably 
  of 
  the 
  Monsoon 
  forest 
  type 
  favoring 
  a 
  more 
  

   distinctly 
  xerophyllous 
  vegetation. 
  

  

  