﻿266 
  G. 
  R. 
  Wieland 
  — 
  On 
  Liassic 
  Floras. 
  

  

  Table 
  I— 
  (Continued). 
  

  

  MlXTECA 
  ALTA 
  

   SPECIES. 
  

  

  Recurrent 
  species. 
  

  

  Affiliated 
  forms. 
  

  

  

  

  Glossopteris 
  indica, 
  Rhatic 
  of 
  Ton- 
  

   kin. 
  

  

  Laccopteris 
  Munsteri, 
  Rhatic, 
  

   Europe. 
  

  

  Sphenopteris 
  Williamsoni, 
  Infer- 
  

   ior 
  Oolite 
  of 
  Yorkshire. 
  

  

  Sagenopteris 
  rhoifolia, 
  Rhatic, 
  

  

  Europe. 
  

   Tozniopteris 
  Danceoides, 
  Damuda 
  

  

  Division, 
  India. 
  

  

  Tceniopteris 
  vittata, 
  Yorkshire 
  

   Lias, 
  Great 
  Oolite. 
  

  

  Laccopteris 
  (?) 
  

  

  Laccopteris 
  near 
  L. 
  

   MiXnsteri 
  in 
  Trias 
  of 
  

   Sonora. 
  

  

  Sphenopteris 
  cf. 
  Wil- 
  

   liamsoni 
  

  

  

  Sagenopteris 
  rhoifolia 
  

  

  

  Tceniopteris 
  cf. 
  Dance- 
  

   oides 
  

  

  

  Tceniopteris 
  Zeilleri 
  _. 
  

  

  Tceniopteris 
  cf. 
  vittata. 
  

  

  Equisetites 
  (Calamites) 
  

  

  Gumbeli 
  

  

  Tceniopteris 
  Zeilleri, 
  

   Rhatic 
  of 
  Tonkin. 
  

  

  Equisetites 
  (Calamites) 
  

   Gumbeli, 
  Upper 
  Trias 
  

   of 
  Franconia. 
  

  

  

  

  (a) 
  Composition 
  of 
  the 
  Mixteca 
  Alta 
  Flora. 
  

  

  In 
  interpreting 
  Table 
  I 
  it 
  is 
  primarily 
  necessary 
  to 
  recall 
  that 
  

   in 
  the 
  plant 
  beds 
  outcropping 
  on 
  the 
  Barranca 
  Consuelo 
  the 
  

   most 
  of 
  the 
  coal 
  occurs 
  near 
  the 
  middle 
  of 
  the 
  lower 
  half 
  of 
  

   the 
  whole 
  thickness 
  of 
  550 
  or 
  more 
  meters 
  ; 
  while 
  the 
  coal 
  is 
  

   followed 
  in 
  the 
  upper 
  portions 
  of 
  *the 
  lower 
  half 
  of 
  the 
  beds 
  by 
  

   a 
  well-marked 
  series 
  of 
  alternating 
  ferruginous 
  sands, 
  shales 
  

   and 
  grits, 
  during 
  the 
  deposition 
  of 
  which 
  changes 
  in 
  the 
  "flora 
  

   seem 
  to 
  have 
  mainly 
  occurred. 
  And 
  it 
  is 
  here 
  that 
  the 
  older 
  

   types 
  of 
  ferns 
  and 
  the 
  Cordaiteans 
  appear 
  to 
  drop 
  out. 
  At 
  

   any 
  rate 
  it 
  becomes 
  w 
  r 
  orth 
  while 
  to 
  further 
  range 
  the 
  plants 
  of 
  

   the 
  lower 
  half 
  of 
  the 
  beds 
  side 
  by 
  side 
  with 
  those 
  of 
  the 
  upper 
  

   half, 
  recalling 
  that 
  the 
  greatest 
  comparatively 
  barren 
  stretches 
  

   in 
  the 
  great 
  section 
  of 
  the 
  Barranca 
  Consuelo 
  plant 
  beds 
  occur 
  

   in 
  the 
  initial 
  and 
  final 
  hundred 
  meters. 
  See 
  the 
  appended 
  

   Table 
  II. 
  

  

  On 
  scanning 
  Table 
  II 
  several 
  most 
  interesting 
  facts 
  appear. 
  

   In 
  the 
  first 
  place 
  it 
  is 
  most 
  surprising 
  that 
  so 
  few 
  of 
  the 
  species 
  

   of 
  the 
  lower 
  half 
  of 
  the 
  Consuelo 
  section 
  continue 
  with 
  cer- 
  

   tainty 
  into 
  the 
  upper 
  half. 
  And 
  this 
  fact, 
  surely 
  not 
  entirely 
  

   due 
  to 
  the 
  fortunes 
  of 
  collecting, 
  appears 
  the 
  more 
  unexpected 
  

   since 
  any 
  division 
  of 
  the 
  beds 
  of 
  the 
  section 
  into 
  a 
  lower 
  and 
  

   upper 
  series 
  would 
  be 
  quite 
  arbitrary. 
  However 
  there 
  are 
  

   observable 
  some 
  changes 
  in 
  dip 
  and 
  deposition, 
  and 
  that 
  con- 
  

   tinuation 
  of 
  study 
  afield 
  which 
  is 
  always 
  urgent 
  may 
  yet 
  reveal 
  

   more 
  than 
  a 
  single 
  unconformity. 
  

  

  