﻿MUDGE.] 
  CRETACEOUS 
  SYSTEM 
  NIOBRARA. 
  283 
  

  

  ject 
  to 
  currents. 
  Sometimes 
  may 
  be 
  seen 
  marked 
  oblique 
  deposits, 
  but 
  

   very 
  limited 
  in 
  extent 
  either 
  vertically 
  or 
  horizontally. 
  These 
  were 
  

   always 
  varied 
  in 
  color 
  and 
  material. 
  Layers 
  of 
  white 
  chalk, 
  with 
  

   impure 
  ones 
  of 
  various^ 
  shades 
  of 
  *buff, 
  extended 
  to 
  a 
  thickness 
  of 
  6 
  to 
  10 
  

   feet, 
  and 
  gave 
  a 
  neat, 
  ribboned 
  appearance. 
  These 
  layers 
  were 
  usually 
  

   from 
  one-fourth 
  to 
  one-half 
  an 
  inch 
  in 
  thickness, 
  but 
  frequently 
  much 
  

   thinner. 
  In 
  one 
  instance 
  I 
  counted 
  thirty-five 
  in 
  a 
  thickness 
  of 
  little 
  

   less 
  than 
  two 
  inches, 
  the 
  white 
  lines 
  being 
  nearly 
  pure 
  chalk, 
  and 
  the 
  

   buff 
  containing 
  some 
  fine 
  sand. 
  The 
  fineness 
  of 
  material 
  and 
  the 
  dis- 
  

   tinctuess 
  of 
  each 
  line 
  indicate 
  a 
  slow 
  deposit 
  at 
  a 
  distance 
  from 
  the 
  

   shores 
  of 
  the 
  old 
  Cretaceous 
  lands. 
  

  

  The 
  shales 
  of 
  this 
  division 
  contain 
  lime 
  mingled 
  with 
  clay 
  and 
  sand 
  

   in 
  varying 
  proportions. 
  They 
  are 
  harder 
  than 
  the 
  chalk, 
  requiring 
  the 
  

   pick 
  in 
  extricating 
  the 
  fossils. 
  They 
  are 
  of 
  all 
  shades 
  of 
  slate-color, 
  

   sometimes 
  bleaching 
  on 
  exposure 
  to 
  the 
  weather. 
  Near 
  Fort 
  Wallace, 
  

   some 
  strata 
  are 
  so 
  much 
  like 
  the 
  Benton 
  in 
  Nebraska, 
  that 
  Professor 
  

   Haydeu, 
  on 
  a 
  hasty 
  inspection, 
  mistook 
  them 
  for 
  a 
  portion 
  of 
  that 
  group. 
  

   (Final 
  Eeport 
  on 
  Nebraska, 
  p. 
  68.) 
  

  

  These 
  shales, 
  in 
  some 
  localities, 
  are 
  traversed 
  by 
  seams, 
  from 
  1 
  to 
  6 
  

   inches 
  in 
  thickness, 
  of 
  firm, 
  pure 
  calc-spar, 
  usually 
  in 
  flat 
  crystals. 
  

   These 
  seams 
  are 
  found 
  in 
  all 
  parts 
  of 
  the 
  Mobrara, 
  though 
  more 
  common 
  

   in 
  the 
  shales 
  than 
  in 
  the 
  chalk 
  strata. 
  When 
  not 
  crystallized 
  the 
  spar 
  

   is 
  harder 
  than 
  usual 
  — 
  apparently 
  not 
  quite 
  as 
  pure. 
  In 
  all 
  case^^, 
  how- 
  

   ever) 
  it 
  will 
  furnish 
  good 
  quicklime, 
  and 
  for 
  that 
  purpose 
  is 
  more 
  con- 
  

   venient 
  than 
  the 
  chalk, 
  as 
  it 
  does 
  not 
  crumble 
  and 
  yield 
  to 
  atmospheric 
  

   influences 
  after 
  burning. 
  The 
  seams 
  were 
  formed 
  by 
  fissures 
  or 
  rents 
  

   in 
  ^he 
  original 
  strata, 
  made 
  probably 
  during 
  their 
  upheaval 
  from 
  the 
  

   ocean-level, 
  and 
  the 
  lime 
  was 
  deposited 
  on 
  both 
  sides 
  of 
  the 
  cavity, 
  and 
  

   usually 
  united 
  in 
  the 
  center, 
  but 
  sometimes 
  the 
  middle 
  is 
  lined 
  by 
  most 
  

   beautiful 
  crystals 
  of 
  calc-spar. 
  The 
  seams 
  being 
  firmer 
  than 
  the 
  chalk, 
  

   stand, 
  like 
  dikes, 
  2 
  or 
  3 
  feet 
  above 
  the 
  surface, 
  not 
  vertically, 
  but 
  inclined 
  

   10° 
  or 
  20° 
  from 
  a 
  perpendicular. 
  Inclosed 
  in 
  these 
  seams 
  are 
  small 
  

   crystals 
  of 
  barite. 
  At 
  Sheridan, 
  Wallace 
  County, 
  we 
  find 
  the 
  latter 
  spar 
  

   in 
  the 
  dark 
  shales. 
  One 
  beautiful 
  crystal, 
  of 
  a 
  rich 
  amber-color, 
  weighed 
  

   eight 
  and 
  one-fourth 
  pounds. 
  

  

  The 
  darker 
  shales 
  also 
  sometimes 
  contain 
  numerous 
  small 
  lenticular 
  

   nodules 
  of 
  pyrites, 
  frequently 
  in 
  fine 
  crystals 
  of 
  various 
  shades 
  of 
  

   brown. 
  

  

  This 
  Niobrara 
  is 
  from 
  75 
  feet 
  in 
  Trego 
  and 
  Ellis 
  counties 
  to 
  200 
  feet 
  

   in 
  Rooks 
  County. 
  The 
  fossils 
  are 
  scattered 
  very 
  similarly 
  in 
  all 
  this 
  

   thickness 
  ; 
  some 
  localities 
  will 
  furnish 
  more 
  from 
  the 
  chalk, 
  while 
  others 
  

   will 
  give 
  more 
  from 
  the 
  shales. 
  We 
  hunt 
  for 
  fossils 
  in 
  all 
  alike, 
  and 
  on 
  

   the 
  whole 
  with 
  equal 
  success. 
  

  

  A 
  few 
  marine 
  plants 
  are 
  found, 
  bpt 
  no 
  land 
  vegetation, 
  except 
  an 
  oc- 
  

   casional 
  fragment 
  of 
  fossil 
  wood. 
  The 
  absence 
  of 
  terrestrial 
  plants 
  is 
  

   the 
  more 
  remarkable, 
  as 
  extinct 
  birds 
  and 
  numerous 
  amphibians 
  indi- 
  

   cate 
  that 
  dry 
  land 
  must 
  have 
  existed. 
  This 
  wood 
  was, 
  in 
  a 
  few 
  in- 
  

   stances 
  bored 
  before 
  fossilization 
  by 
  some 
  small 
  animal. 
  This 
  might 
  

   have 
  been 
  done 
  by 
  the 
  larva 
  of 
  an 
  insect 
  (a 
  " 
  borer,") 
  when 
  the 
  tree 
  

   was 
  living, 
  or 
  later 
  by 
  a 
  teredo* 
  when 
  the 
  trunk 
  floated 
  in 
  water. 
  In 
  

   either 
  case 
  it 
  shows 
  that 
  the 
  Cretaceous 
  vegetation 
  was 
  subject 
  to 
  the 
  

   same 
  enemies 
  as 
  that 
  of 
  the 
  present 
  period. 
  Some 
  of 
  this 
  wood 
  was 
  in 
  

   a 
  charred 
  condition, 
  and 
  would 
  burn 
  freely. 
  Other 
  specimens 
  were 
  

   changed 
  to 
  almost 
  pure 
  silica, 
  the 
  cavities 
  studded 
  with 
  crystals 
  of 
  

   quartz. 
  In 
  one 
  case 
  a 
  log, 
  weighing 
  about 
  500 
  pounds, 
  had 
  all 
  condi- 
  

  

  *A 
  teredo, 
  T. 
  tihiaUs, 
  has 
  beou 
  found 
  in 
  the 
  Cretaceous 
  of 
  Alabama. 
  

  

  