﻿186 
  W. 
  T. 
  Lee 
  — 
  Type 
  Section 
  of 
  Morrison 
  Formation. 
  

  

  vary 
  in 
  thickness, 
  disappearing 
  entirely 
  in 
  some 
  places, 
  

   while 
  in 
  others 
  the 
  thickness 
  increases 
  to 
  more 
  than 
  100 
  

   feet. 
  In 
  northern 
  Colorado 
  they 
  contain 
  Ostrea 
  sp. 
  and 
  

   fragments 
  of 
  Pentacrinus 
  asteriscus. 
  3 
  In 
  brief, 
  mem- 
  

   bers 
  8-10 
  of 
  the 
  section 
  must 
  be 
  referred 
  to 
  the 
  Sundance 
  

   formation 
  of 
  the 
  Jurassic. 
  

  

  "When 
  the 
  strata 
  at 
  Morrison 
  were 
  first 
  described 
  as 
  

   Atlantosaurus 
  Beds 
  (later 
  named 
  Morrison), 
  separating 
  

   Eed 
  Beds 
  below 
  from 
  Dakota 
  above, 
  the 
  formational 
  

   boundaries 
  were 
  based 
  on 
  conspicuous 
  lithologic 
  

   changes. 
  Perhaps 
  the 
  quartzose 
  nature 
  of 
  "lower 
  

   Dakota' 
  ' 
  is 
  not 
  so 
  important 
  in 
  determining 
  formational 
  

   boundaries 
  as 
  the 
  conglomeratic 
  nature 
  of 
  the 
  Saurian 
  

   conglomerate. 
  Indeed, 
  Eldridge 
  seems 
  to 
  have 
  consid- 
  

   ered 
  this 
  conglomerate 
  as 
  the 
  possible 
  base 
  of 
  Dakota, 
  

   for 
  in 
  his 
  description 
  in 
  the 
  Denver 
  Monograph 
  (p. 
  61) 
  

   he 
  refers 
  to 
  the 
  difficulty 
  of 
  distinguishing 
  it 
  from 
  the 
  

   lower 
  Dakota 
  of 
  neighboring 
  regions. 
  However, 
  this 
  

   reference 
  would 
  necessitate 
  distinguishing 
  the 
  dinosaurs 
  

   of 
  this 
  conglomerate 
  from 
  those 
  of 
  the 
  Morrison 
  as 
  here 
  

   restricted 
  or 
  accounting 
  for 
  them 
  as 
  reworked 
  material 
  

   from 
  the 
  older 
  beds. 
  This 
  question 
  must 
  be 
  decided 
  by 
  

   the 
  vertebrate 
  paleontologists. 
  

  

  In 
  order 
  to 
  compare 
  the 
  rocks 
  at 
  Morrison 
  with 
  those 
  

   of 
  neighboring 
  localities, 
  I 
  followed 
  the 
  outcrop 
  for 
  

   several 
  miles 
  both 
  north 
  and 
  south 
  of 
  that 
  town. 
  To 
  the 
  

   south 
  for 
  a 
  distance 
  of 
  about 
  10 
  miles 
  they 
  are 
  not 
  so 
  

   well 
  exposed 
  as 
  I 
  had 
  hoped 
  to 
  find 
  them. 
  The 
  Jurassic 
  

   beds 
  Nos. 
  8-10 
  of 
  the 
  section 
  were 
  not 
  positively 
  identi- 
  

   fied 
  and 
  no 
  stratum 
  was 
  found 
  within 
  what 
  is 
  there 
  called 
  

   Morrison 
  that 
  could 
  be 
  correlated 
  with 
  the 
  Saurian 
  con- 
  

   glomerate. 
  It 
  is 
  possible, 
  however, 
  that 
  this 
  conglom- 
  

   erate 
  corresponds 
  with 
  the 
  one 
  which 
  is 
  there 
  called 
  

   "lower 
  Dakota.' 
  ' 
  Still 
  farther 
  south 
  in 
  the 
  Castle 
  Rock 
  

   quadrangle 
  the 
  conglomeratic 
  sandstone 
  and 
  the 
  shale 
  

   above 
  it 
  have 
  been 
  referred 
  to 
  the 
  Lower 
  Cretaceous. 
  

  

  The 
  formations 
  under 
  study 
  are 
  better 
  exposed 
  north 
  

   of 
  Morrison. 
  There 
  I 
  traced 
  the 
  several 
  lithologic 
  units 
  

   of 
  the 
  Morrison 
  section 
  along 
  the 
  hogback 
  as 
  far 
  as 
  the 
  

   town 
  of 
  Golden. 
  About 
  two 
  miles 
  south 
  of 
  that 
  town 
  

   the 
  so-called 
  Dakota 
  fire-clay 
  has 
  been 
  mined 
  in 
  several 
  

   places, 
  making 
  excellent 
  exposures. 
  At 
  the 
  old 
  work- 
  

  

  8 
  Hayden, 
  F. 
  V., 
  U. 
  S. 
  Geol. 
  Survey 
  of 
  Colorado 
  and 
  New 
  Mexico 
  (Third 
  

   Ann. 
  Kept.), 
  p. 
  19, 
  1869. 
  

  

  