﻿Geology 
  and 
  Mineralogy. 
  71 
  

  

  (Upper 
  Cretaceous 
  No. 
  1). 
  Farther, 
  the 
  cycad 
  trunk 
  horizon, 
  

   which 
  at 
  Minnekahta 
  is 
  from 
  60 
  to 
  100 
  feet 
  below 
  this, 
  and 
  175 
  

   feet 
  above 
  the 
  horizon 
  of 
  Barosaurus 
  in 
  the 
  Atlantosaurus 
  Beds 
  

   of 
  Marsh, 
  is 
  held 
  to 
  be 
  Lower 
  Cretaceous, 
  — 
  probably 
  the 
  equiva- 
  

   lent 
  of 
  the 
  Xeocomian 
  or 
  the 
  Wealden. 
  At 
  the 
  Black 
  Hawk 
  

   cycad 
  locality 
  the 
  conditions 
  are 
  found 
  to 
  be 
  essentially 
  similar. 
  

  

  It 
  certainly 
  cannot 
  be 
  amiss 
  to 
  point 
  out 
  that 
  we 
  are 
  here 
  con- 
  

   cerned 
  with 
  eighty-seven 
  species 
  of 
  plants 
  scarcely 
  a 
  genus 
  of 
  

   which 
  does 
  not 
  have 
  its 
  Jurassic 
  representative, 
  excluding 
  of 
  

   course 
  some 
  half 
  dozen 
  plants 
  from 
  just 
  below 
  the 
  Fort 
  Benton, 
  

   which 
  are 
  apparently 
  Upper 
  Cretaceous. 
  In 
  the 
  lower 
  portion 
  of 
  

   the 
  strata 
  in 
  question, 
  especially 
  in 
  the 
  Hay 
  Creek 
  region, 
  some 
  

   distinctly 
  Jurassic 
  plants 
  are 
  present, 
  and 
  when 
  the 
  flora 
  is 
  more 
  

   fully 
  known 
  they 
  may 
  prove 
  to 
  be 
  more 
  than 
  mere 
  "survivors," 
  

   as 
  Professor 
  Ward 
  suggests. 
  As 
  has 
  been 
  stated 
  by 
  Professor 
  

   Marsh, 
  the 
  Cycads 
  of 
  Wyoming, 
  200 
  miles 
  farther 
  west 
  where 
  

   the 
  faunal 
  conditions 
  are 
  held 
  to 
  be 
  essentially 
  similar 
  to 
  those 
  in 
  

   the 
  immediate 
  vicinity 
  of 
  the 
  Black 
  Hills, 
  are 
  certainly 
  Jurassic. 
  

   Moreover, 
  in 
  additiou 
  to 
  Barosaurus 
  from 
  a 
  lower 
  horizon, 
  the 
  

   strata 
  on 
  the 
  eastern 
  side 
  of 
  " 
  the 
  hills 
  " 
  contain 
  a 
  Dinosaurian 
  

   genus 
  closely 
  allied 
  to 
  Stegosaurus 
  at 
  a 
  distance 
  of 
  at 
  least 
  150 
  

   feet 
  above 
  the 
  marine 
  Jurassic. 
  Between 
  this 
  and 
  the 
  Cycads 
  

   there 
  are 
  scarcely 
  100 
  feet 
  of 
  intervening 
  strata, 
  and 
  no 
  breaks 
  are 
  

   discernible. 
  All 
  is 
  continuous 
  deposition. 
  The 
  scantiness 
  of 
  

   knowledge 
  regarding 
  both 
  the 
  faunal 
  and 
  floral 
  record, 
  the 
  diffi- 
  

   culty 
  of 
  defining 
  the 
  limits 
  of 
  the 
  European 
  Jurassic, 
  and 
  the 
  fact 
  

   that 
  these 
  strata 
  though 
  delimited 
  by 
  those 
  two 
  great 
  landmarks, 
  — 
  

   the 
  marine 
  Jurassic 
  and 
  Fort 
  Benton, 
  are 
  all 
  fresh 
  water, 
  make 
  it 
  

   clear 
  that 
  the 
  physical 
  record 
  must 
  also 
  be 
  taken 
  into 
  considera- 
  

   tion. 
  There 
  are 
  good 
  reasons 
  for 
  believing 
  that 
  here 
  exists 
  an 
  

   extensive 
  development 
  of 
  distinctly 
  fresh-water 
  Jurassic 
  followed 
  

   by 
  Wealden 
  equivalents. 
  It 
  is 
  not 
  to 
  be 
  forgotten 
  that 
  farther 
  

   west 
  the 
  corresponding 
  strata 
  are 
  much 
  thicker. 
  Hence 
  to 
  state 
  

   now 
  that 
  a 
  Wealden 
  or 
  a 
  Lower 
  Cretaceous 
  equivalent 
  begins 
  a 
  

   little 
  below 
  the 
  cycad 
  horizon, 
  or 
  perhaps 
  with 
  the 
  " 
  quartzitic 
  

   cap" 
  just 
  above 
  this 
  which 
  still 
  contains 
  large 
  fossil 
  trees 
  as 
  seen 
  

   in 
  the 
  Black 
  Hawk 
  locality, 
  would 
  mean 
  the 
  assuming 
  of 
  a 
  diffi- 
  

   cult 
  position. 
  Unfortunately 
  the 
  conditions 
  which 
  in 
  localities 
  

   like 
  the 
  Hay 
  Creek 
  region 
  were 
  favorable 
  for 
  the 
  preservation 
  of 
  

   cycadean 
  foliage 
  were 
  unfavorable 
  to 
  the 
  preservation 
  of 
  trunks, 
  

   and 
  where 
  the 
  latter 
  occur 
  the 
  leaves 
  appear 
  to 
  have 
  been 
  mostly 
  

   destroyed. 
  These 
  two 
  facts 
  have 
  thus 
  far 
  prevented 
  our 
  gaining 
  

   a 
  more 
  exact 
  knowledge 
  of 
  the 
  vertical 
  distribution 
  of 
  the 
  Cycads. 
  

   While 
  Professor 
  Ward 
  finds 
  ground 
  for 
  a 
  final 
  decision 
  that 
  the 
  

   Cycads 
  of 
  the 
  Black 
  Hills 
  are 
  not 
  Jurassic, 
  in 
  view 
  of 
  these 
  ele- 
  

   ments 
  of 
  uncertainty 
  their 
  age 
  will 
  doubtless 
  form 
  the 
  subject 
  of 
  

   further 
  discussion. 
  G. 
  R. 
  W. 
  

  

  9. 
  Les 
  Variations 
  periodiques 
  des 
  Glaciers, 
  4me 
  Rapport, 
  

   1898, 
  redige 
  par 
  E. 
  Richter. 
  — 
  This 
  fourth 
  Report 
  of 
  the 
  Inter- 
  

   national 
  Commission 
  on 
  Glaciers 
  has 
  recently 
  been 
  published 
  in 
  

  

  