﻿MUDGE.] 
  TERTIARY 
  SYSTEM 
  PLIOCKNE, 
  279 
  

  

  and 
  in 
  slides 
  we 
  frequently 
  found 
  them 
  intermingled. 
  The 
  contrast 
  

   was 
  remarkable, 
  as 
  hardly 
  a 
  single 
  type 
  was 
  common 
  to 
  both. 
  

  

  The 
  material 
  of 
  the 
  Pliocene 
  deposits 
  consists 
  of 
  sandstone 
  of 
  various 
  

   shades 
  of 
  gray 
  and 
  brown, 
  occasionally 
  whitened 
  by 
  a 
  small 
  admixture 
  

   of 
  lime. 
  The 
  lower 
  strata 
  are 
  usually 
  composed 
  of 
  finer 
  sand 
  than 
  the 
  

   upper, 
  and 
  much 
  more 
  loose 
  and 
  friable 
  in 
  their 
  texture. 
  The 
  overlying 
  

   beds 
  are 
  of 
  coarser 
  ingredients, 
  consisting 
  of 
  water-worn 
  pebbles 
  of 
  

   metamorphic 
  rocks 
  — 
  quartz, 
  greenstone, 
  granite, 
  syenite, 
  and 
  sometimes 
  

   fragments 
  of 
  fossil 
  wood 
  from 
  an 
  older 
  formation. 
  These 
  portions 
  of 
  

   the 
  deposit 
  when 
  crumbled 
  and 
  the 
  finer 
  parts 
  washed 
  awa,y, 
  have 
  

   much 
  the 
  appearance 
  of 
  diift, 
  and 
  have 
  been 
  mistaken 
  for 
  it. 
  This 
  

   formation, 
  down 
  to 
  a 
  recent 
  period, 
  must 
  have 
  covered 
  the 
  whole 
  of 
  the 
  

   Cretaceous, 
  as 
  we 
  find 
  the 
  coarser 
  pebbles 
  scattered, 
  to 
  a 
  greater 
  or 
  less 
  

   extent, 
  over 
  the 
  western 
  half 
  of 
  the 
  State. 
  It 
  must 
  have 
  been 
  subject 
  

   to 
  later 
  movements 
  of 
  water-currents, 
  as 
  it 
  assumes 
  the 
  form 
  of 
  altered 
  

   drift, 
  and 
  sometimes 
  includes 
  remains 
  of 
  the 
  mastodon 
  and 
  elephant, 
  

   of 
  the 
  later 
  Quaternary 
  age. 
  

  

  The 
  sandstone 
  is 
  usually 
  friable, 
  crumbling 
  on 
  exposure 
  to 
  the 
  atmos- 
  

   phere. 
  When 
  more 
  compact, 
  its 
  mechanical 
  construction 
  is 
  so 
  irregu- 
  

   lar 
  as 
  to 
  render 
  it 
  almost 
  entirely 
  unfit 
  for 
  a 
  building-material. 
  When 
  

   firmly 
  consolidated, 
  it 
  forms 
  the 
  hill-tops 
  of 
  the 
  table-like 
  eminences 
  

   along 
  the 
  line 
  of 
  the 
  boundary 
  of 
  the 
  Pliocene 
  and 
  Cretaceous 
  forma- 
  

   tions. 
  

  

  At 
  Breadbowl 
  Mound, 
  Phillips 
  County, 
  it 
  is 
  about 
  200 
  feet 
  above 
  

   Deer 
  Creek, 
  and 
  at 
  Sugarloaf 
  Mound, 
  in 
  the 
  western 
  part 
  of 
  Rooks 
  

   County, 
  it 
  is 
  about 
  300 
  feet 
  above 
  the 
  Solomon 
  River. 
  In 
  these 
  hills, 
  

   as 
  in 
  many 
  others, 
  the 
  upper 
  strata 
  belong 
  to 
  the 
  Pliocene, 
  while 
  the' 
  

   bases 
  are 
  of 
  the 
  Niobrara. 
  Farther 
  west 
  it 
  forms 
  the 
  whole 
  of 
  the 
  visi- 
  

   ble 
  outcrop, 
  and 
  the 
  mounds 
  are 
  not 
  so 
  prominent. 
  

  

  .On 
  Prairie 
  Dog 
  Creek, 
  in 
  ISTorton 
  County, 
  it 
  is 
  400 
  feet 
  in 
  thickness, 
  

   and 
  in 
  the 
  extreme 
  northwestern 
  part 
  of 
  the 
  State 
  we 
  have 
  reason 
  to 
  

   believe 
  it 
  is 
  still 
  thicker. 
  The 
  various 
  strata 
  are 
  not 
  clearly 
  defined 
  or 
  

   regular 
  in 
  line 
  of 
  deposit, 
  and 
  the 
  continued 
  thickness 
  cannot 
  be 
  easily 
  

   discovered. 
  The 
  formation, 
  like 
  all 
  others 
  in 
  the 
  State, 
  appears 
  to 
  dip 
  

   slightly 
  to 
  the 
  northwest. 
  It 
  is 
  conformably, 
  or 
  nearly 
  so, 
  upon 
  the 
  

   Cretaceous. 
  

  

  Iq 
  the 
  southern 
  portion 
  of 
  the 
  Pliocene, 
  in 
  the 
  vicinity 
  of 
  Fort 
  Wal- 
  

   lace 
  and 
  Sheridan, 
  the 
  hill-tops 
  are 
  covered 
  with 
  a 
  stratum 
  about 
  8 
  

   feet 
  in 
  thickness, 
  very 
  hard 
  and 
  siliceous. 
  The 
  material 
  varies 
  from 
  

   coarse 
  flint-qiiartz 
  to 
  chalcedony. 
  The 
  latter 
  mineral 
  shades 
  from 
  milk- 
  

   white 
  to 
  transparent, 
  sometimes 
  presenting 
  a 
  semi-opal 
  appearance. 
  

   The 
  so-called 
  moss 
  agate 
  is 
  found 
  in 
  the 
  upper 
  few 
  inches 
  of 
  the 
  stratum. 
  

   This 
  cap 
  rock 
  is 
  interesting 
  to 
  the 
  mineralogist 
  by 
  showing 
  the 
  moss 
  

   agate 
  in 
  its 
  various 
  stages 
  of 
  formation. 
  The 
  lower 
  portion 
  of 
  the 
  8 
  feet 
  

   indicates 
  an 
  imperfect 
  chemical 
  solution 
  of 
  the 
  silica 
  and 
  black 
  oxide 
  of 
  

   manganese, 
  therefore 
  the 
  crystallization 
  of 
  the 
  latter 
  is 
  imperfect. 
  As 
  

   we 
  examine 
  the 
  stratum 
  from 
  the 
  bottom 
  to 
  the 
  top, 
  we 
  find 
  the 
  chem- 
  

   ical 
  conditions 
  more 
  favorable 
  and 
  complete, 
  so 
  that 
  the 
  distinct 
  quartz, 
  

   chalcedony, 
  and 
  manganese 
  of 
  the 
  bottom 
  become 
  more 
  commingled 
  to- 
  

   ward 
  the 
  upper 
  inch 
  or 
  half 
  inch, 
  where 
  the 
  silica 
  must 
  have 
  been 
  suf- 
  

   ficiently 
  fluid 
  to 
  allow 
  the 
  manganese* 
  to 
  assume 
  the 
  form 
  of 
  sprig 
  crys- 
  

   tals. 
  This 
  peculiar 
  deposit 
  is 
  common 
  on 
  all 
  the 
  high 
  hill 
  tops 
  of 
  Wal- 
  

   lace 
  County, 
  but 
  the 
  best 
  locality 
  is 
  the 
  cap-rock 
  of 
  the 
  two 
  buttes, 
  two 
  

   miles 
  southwest 
  of 
  Sheridan, 
  and 
  half 
  a 
  mile 
  from 
  the 
  line 
  of 
  the 
  Kan- 
  

   sas 
  Pacific 
  Railway. 
  They 
  form 
  a 
  notable 
  landmark 
  to 
  travelers. 
  

  

  *0n 
  a 
  chemical 
  test 
  by 
  Prof. 
  W. 
  K. 
  Kedzie, 
  some 
  iron 
  was 
  found 
  with 
  the 
  manganese. 
  

  

  