﻿T. 
  E. 
  Savage 
  — 
  Devonian 
  Formation 
  of 
  Illinois. 
  181 
  

  

  also 
  collected 
  Hypothyris 
  cuboides 
  from 
  the 
  limestone 
  a 
  

   few 
  feet 
  above 
  the 
  Acervularia 
  davidsoni 
  coral 
  reef 
  in 
  

   Fayette 
  County, 
  Iowa. 
  

  

  ^Begarding 
  the 
  age 
  of 
  the 
  Wapsipinicon 
  and 
  Cedar 
  

   Valley 
  limestones, 
  it 
  is 
  significant 
  that 
  in 
  Iowa 
  and 
  

   northwest 
  Illinois 
  Spirifer 
  subumbonus 
  occurs 
  in 
  abun- 
  

   dance 
  in 
  the 
  basal 
  layers 
  of 
  the 
  Wapsipinicon 
  limestone, 
  

   and 
  Hypothyris 
  cuboides, 
  and 
  H. 
  intermedia 
  which 
  is 
  

  

  Fig. 
  3. 
  

  

  Fig. 
  3. 
  — 
  View 
  of 
  the 
  lower 
  part 
  of 
  the 
  Cedar 
  Valley 
  limestone, 
  near 
  

   Milan, 
  Eock 
  Island 
  County, 
  Illinois. 
  

  

  regarded 
  as 
  a 
  synonym 
  for 
  H. 
  cuboides, 
  are 
  present 
  in 
  

   the 
  lower 
  part 
  of 
  this 
  formation 
  at 
  Davenport 
  and 
  occur 
  

   also 
  in 
  the 
  Cedar 
  Valley 
  limestone 
  above 
  the 
  coral 
  reef. 
  

   These 
  species 
  are 
  characteristic 
  of 
  the 
  early 
  upper 
  

   Devonian 
  rocks 
  (Tully 
  limestone) 
  in 
  New 
  York, 
  and 
  it 
  

   is 
  thought 
  that 
  the 
  Wapsipinicon 
  and 
  the 
  overlying 
  

   Cedar 
  Valley 
  limestones 
  in 
  the 
  Iowa, 
  northwest 
  Illinois, 
  

   and 
  northern 
  Missouri 
  region 
  should 
  be 
  correlated 
  with 
  

  

  