﻿GEOLOGY. 
  271 
  

  

  nautilus, 
  bellerophon, 
  and 
  bacculitis 
  ftiujasii, 
  are 
  nume- 
  

   rous 
  in 
  the 
  lowest 
  exposed 
  strata 
  of 
  micaceous 
  shale 
  and 
  

   green-sand, 
  which 
  forms 
  the 
  base 
  of 
  the 
  talus, 
  and 
  in 
  

   which 
  the 
  Exogera 
  Costata 
  are 
  profusely 
  deposited, 
  hav- 
  

   ing 
  fallen 
  from 
  the 
  superior 
  strata 
  in 
  the 
  escarpment 
  of 
  

   the 
  bluff 
  where 
  they 
  are 
  seen 
  horizontally 
  disposed 
  in 
  

   place. 
  

  

  From 
  the 
  character 
  of 
  the 
  bed 
  in 
  which 
  they 
  are 
  

   found, 
  it 
  is 
  difficult 
  to 
  extract 
  the 
  casts 
  from 
  the 
  matrix, 
  

   and 
  but 
  few, 
  chiefly 
  those 
  of 
  the 
  Catillus, 
  were 
  obtained. 
  

   The 
  exogera, 
  however, 
  are 
  of 
  different 
  character, 
  be- 
  

   ing 
  mineralized 
  nearly 
  to 
  silicification. 
  The 
  shells 
  de- 
  

   tach 
  themselves 
  readily 
  from 
  the 
  strata, 
  and 
  are 
  found 
  

   also 
  strewn 
  profusely 
  on 
  the 
  surface 
  of 
  the 
  adjacent 
  

   prairies, 
  and 
  in 
  the 
  small 
  superficial 
  channels 
  and 
  ravines 
  

   at 
  a 
  prairie 
  bluff; 
  two 
  miles 
  further, 
  near 
  the 
  Oktibbeha 
  

   Creek, 
  where 
  the 
  gryphjea 
  globosa 
  and 
  a 
  peculiar 
  small 
  

   hook-shaped 
  fossil, 
  the 
  Hamulus 
  onyx, 
  are 
  also 
  found, 
  

   the 
  latter 
  similarly 
  dispersed 
  in 
  great 
  quantities. 
  

  

  At 
  the 
  base 
  of 
  this 
  bluff, 
  near 
  the 
  water's 
  edge, 
  ledges 
  

   of 
  conglomerate, 
  formed 
  chiefly 
  of 
  the 
  exogera, 
  are 
  ex- 
  

   posed, 
  and 
  at 
  Plymouth 
  Bluff" 
  the 
  pecten 
  quinque 
  costa- 
  

   tus 
  was 
  found 
  among 
  the 
  other 
  fossils. 
  

  

  Near 
  Aberdeen, 
  ammonites, 
  changed 
  to 
  a 
  compact 
  

   calcareous 
  rock, 
  have 
  been 
  found 
  of 
  large 
  size. 
  I 
  met 
  

   with 
  some 
  considerable 
  sections 
  of 
  these, 
  divided 
  by 
  the 
  

   transverse 
  plates 
  or 
  partitions 
  of 
  the 
  cells, 
  and 
  suscepti- 
  

   ble 
  of 
  being 
  fitted 
  together 
  or 
  reunited 
  at 
  their 
  joints 
  or 
  

   lines 
  of 
  separation. 
  

  

  The 
  lamna 
  cuspidata 
  of 
  Agassiz, 
  has 
  also 
  been 
  found 
  

   in 
  the 
  prairie 
  rock 
  near 
  Aberdeen. 
  

  

  At 
  Okolona, 
  the 
  gryphoea 
  globosa 
  was 
  seen 
  in 
  the 
  

   white 
  limestone 
  excavated 
  from 
  the 
  deep 
  well 
  in 
  that 
  

   place; 
  the 
  shells 
  all 
  having 
  a 
  black 
  slaty 
  aiDpearance, 
  

  

  