﻿PEALE.] 
  MESOZOIC 
  FORMATIONS 
  JURASSIC 
  CRETACEOUS. 
  87 
  

  

  The 
  following 
  are 
  lists 
  of 
  fossils 
  from 
  the 
  Jurassic 
  strata 
  described 
  in 
  

   those 
  sections 
  : 
  

  

  Howell 
  and 
  others 
  in 
  Southern 
  Utah. 
  Powoll 
  in 
  Plateau 
  Province. 
  

  

  Pentacrinus 
  asieriscus. 
  Fentacrinus 
  asferiscus. 
  

  

  Ostrea 
  strigilecula. 
  Ostrea 
  3trigilecula. 
  

  

  Camptonectes 
  stygius. 
  Camptonectes 
  stygius. 
  

  

  bellistriatus. 
  helUstriatus. 
  

  

  Bioceramus 
  crassalatus. 
  platessiformis. 
  

  

  Myophoria 
  amhilineata. 
  MyopJioria 
  f 
  

  

  Trigonia 
  ? 
  Trigonia 
  

  

  Neritina 
  f 
  phaseolaris. 
  Trigonia 
  americana. 
  

  

  montanensis. 
  

   Gonradi. 
  

  

  Trigonella 
  ? 
  

  

  Neritina 
  ff 
  Powelli. 
  

  

  Rhynclionella 
  gnathopJiora. 
  

  

  myrina. 
  

   Ostrea 
  (Alectryonia) 
  procumbens. 
  

  

  Gervillea 
  f 
  

  

  Pinna 
  f 
  

  

  Myacites 
  

  

  Belemnites 
  densus. 
  

   Ammonites 
  cordiformis. 
  

   Undetermined 
  (Jonchifers 
  and 
  Gastero- 
  

   pods. 
  

  

  As 
  I 
  have 
  already 
  stated, 
  Professor 
  Newberry 
  found 
  plants 
  at 
  the 
  top 
  

   of 
  the 
  variegated 
  series, 
  and 
  refers 
  the 
  whole 
  gypsum 
  series 
  to 
  the 
  Tri- 
  

   assic; 
  and 
  Professor 
  White 
  noticed 
  fossils 
  found 
  by 
  Mr. 
  Howell 
  at 
  

   the 
  base 
  of 
  the 
  Triassic, 
  and 
  says 
  they 
  are 
  of 
  Jurassic 
  affinity. 
  It 
  seems, 
  

   therefore, 
  a 
  disputed 
  point 
  whether 
  we 
  should 
  consider 
  both 
  periods 
  rep- 
  

   resented-, 
  and 
  call 
  the 
  formation 
  Jura-Trias, 
  as 
  Powell 
  has 
  done, 
  or 
  treat 
  

   them 
  as 
  two 
  distinct 
  formations. 
  

  

  Mr. 
  Howell 
  is 
  of 
  the 
  opinion 
  that 
  the 
  Jurassic 
  thins 
  out, 
  and 
  proba- 
  

   bly 
  disappears 
  in 
  Eastern 
  Arizona 
  and 
  New 
  Mexico. 
  I 
  think 
  that 
  the 
  

   sections 
  show 
  that 
  it 
  is 
  probably 
  present, 
  although 
  it 
  is 
  difficult 
  to 
  define 
  

   it 
  at 
  all 
  localities, 
  as 
  the 
  rocks 
  grade 
  into 
  those 
  that 
  belong 
  to 
  the 
  Cre- 
  

   taceous 
  above 
  and 
  the 
  Triassic 
  below. 
  

  

  In 
  the 
  future 
  we 
  may 
  have 
  to 
  consider 
  the 
  whole 
  formation 
  as 
  Jurassic. 
  

   It 
  may 
  be 
  that 
  the 
  fossils 
  represent 
  both 
  the 
  formations. 
  In 
  Eastern 
  

   North 
  America 
  the 
  line 
  between 
  them 
  has 
  not 
  been 
  definitely 
  drawn, 
  

   and 
  in 
  the 
  West 
  we 
  will 
  have 
  to 
  wait 
  until 
  we 
  have 
  more 
  evidence. 
  At 
  

   present, 
  it 
  seems 
  to 
  be 
  in 
  favor 
  of 
  the 
  Jurassic. 
  

  

  CRETACEOUS. 
  

  

  The 
  Cretaceous 
  strata 
  in 
  our 
  district 
  are 
  comprehended 
  under 
  the 
  

   Lower 
  division, 
  (Dakota 
  group,) 
  Middle 
  division, 
  and 
  the 
  base 
  of 
  the 
  

   Upper 
  division. 
  The 
  latter 
  is 
  exposed 
  at 
  only 
  one 
  locality, 
  and 
  the 
  mid- 
  

   dle 
  division 
  is 
  only 
  partially 
  seen 
  at 
  most 
  localities. 
  The 
  Dakota 
  group 
  

   is 
  the 
  only 
  formation 
  occupying 
  much 
  area 
  in 
  the 
  district. 
  

  

  In 
  the 
  table 
  given 
  on 
  page 
  128 
  of 
  the 
  Eeport 
  of 
  United 
  States 
  Geologi- 
  

   cal 
  Survey 
  for 
  1873, 
  I 
  included 
  the 
  Fort 
  Pierre 
  group 
  (No. 
  4) 
  in 
  the 
  Mid- 
  

   dle 
  Cretaceous, 
  because 
  I 
  was 
  unable 
  to 
  draw 
  any 
  line 
  between 
  No. 
  3 
  

  

  