﻿GEOLOGY. 
  275 
  

  

  substance, 
  and 
  assumes 
  a 
  grayish 
  appearance, 
  owing 
  to 
  the 
  

   large 
  proportion 
  of 
  finely 
  comminuted 
  shell 
  contained 
  in 
  it. 
  

  

  The 
  quantity 
  of 
  entire 
  shells 
  imbedded 
  in 
  it 
  is 
  very 
  

   great, 
  lying 
  almost 
  in 
  contact 
  with 
  each 
  other, 
  and 
  form- 
  

   ing 
  perhaps 
  one-sixth 
  of 
  the 
  volume 
  of 
  the 
  deposit. 
  

  

  When 
  first 
  exposed, 
  these 
  shells 
  present 
  a 
  lively 
  

   yellow 
  tint, 
  but 
  become 
  somewhat 
  bleached 
  and 
  changed 
  

   to 
  a 
  dull 
  white 
  by 
  exposure. 
  

  

  Of 
  more 
  than 
  forty 
  species 
  that 
  have 
  been 
  found, 
  

   very 
  few 
  are 
  identical 
  with 
  those 
  of 
  Vicksburg, 
  and 
  

   many 
  of 
  them 
  belong 
  to 
  distinct 
  genera. 
  Generally, 
  they 
  

   exceed 
  the 
  Vicksburg 
  shells 
  considerably 
  in 
  size. 
  

  

  Among 
  them 
  the 
  Rostellaria 
  velata 
  of 
  Conrad 
  is 
  by 
  

   far 
  the 
  most 
  abundant, 
  amounting 
  perhaps 
  to 
  twenty-five 
  

   per 
  cent, 
  of 
  the 
  whole 
  number. 
  

  

  An 
  unusually 
  large 
  Mytra 
  is 
  also 
  found 
  here; 
  for 
  

   which, 
  it 
  proving 
  to 
  be 
  new, 
  I 
  propose 
  the 
  specific 
  name 
  

   Millingtonii, 
  in 
  respect 
  to 
  my 
  friend, 
  Doctor 
  Millington, 
  

   first 
  principal 
  geologist 
  of 
  the 
  State. 
  

  

  A 
  Cyprgea 
  (fenestrela) 
  having 
  the 
  exterior 
  surface 
  

   covered 
  with 
  a 
  double 
  series 
  of 
  fine, 
  but 
  very 
  distinct 
  

   stria, 
  intersecting 
  and 
  crossing 
  each 
  other, 
  seems 
  to 
  be 
  

   peculiar 
  to 
  this 
  bed, 
  but 
  its 
  greatest 
  novelty 
  is 
  a 
  large 
  

   depressed 
  patelliform 
  shell, 
  belonging 
  to 
  the 
  genus 
  Um- 
  

   brella 
  of 
  Swainson, 
  and 
  for 
  which 
  planulata 
  is 
  proposed 
  

   by 
  Mr. 
  Conrad 
  as 
  the 
  specific 
  name. 
  

  

  The 
  foregoing, 
  together 
  with 
  the 
  phorus 
  reclusus 
  may 
  

   be 
  considered 
  the 
  characteristic 
  shells 
  of 
  the 
  deposit. 
  

  

  Two 
  species 
  of 
  turbinoba, 
  a 
  large 
  flabellum, 
  and 
  two 
  

   species 
  of 
  the 
  oyster, 
  one 
  of 
  which, 
  of 
  large 
  size 
  and 
  to 
  

   some 
  extent 
  silicified, 
  is 
  also 
  of 
  common 
  occurrence 
  on 
  

   the 
  surface 
  in 
  the 
  vicinity, 
  and 
  abundantly 
  in 
  the 
  small 
  

   prairie 
  half 
  a 
  mile 
  northeast 
  of 
  the 
  State 
  House, 
  are 
  also 
  

   included 
  in 
  this 
  remarkable 
  group 
  of 
  fossils. 
  

  

  