﻿

  Geology 
  and 
  Natural 
  History. 
  387 
  

  

  Potomac 
  formation 
  of 
  Maryland 
  (Upper 
  Jurassic?). 
  — 
  Cycadeoidea 
  Marylandica 
  

   Fontaine, 
  Tysoniana, 
  Fontaineano, 
  McGeeana, 
  fflileri, 
  Bibbinsi. 
  and 
  Gouch- 
  

   eriana 
  (last 
  6 
  species 
  Ward). 
  

  

  Trinity 
  Beds 
  (Comanche 
  Series), 
  Cheyenne 
  Rock. 
  Belvidere, 
  Southern 
  Kansas, 
  — 
  

   Cycadeoidea 
  munita 
  Cragin. 
  

  

  Pre 
  (?) 
  Laramie 
  near 
  Golden, 
  Colorado, 
  — 
  Cycadeoidea 
  mirabilis 
  Lesquereux. 
  

  

  Upper 
  Trias. 
  Xorth 
  Carolina, 
  locality 
  lost, 
  — 
  Cycadeoidea 
  Emmonsi 
  Fontaine. 
  

  

  Trias 
  of 
  Prince 
  Edward's 
  Isle, 
  — 
  Cycadeoidea 
  abiquidensis 
  Dawson. 
  

  

  About 
  35 
  species 
  of 
  cycadean 
  trunks, 
  probably 
  all 
  belonging 
  to 
  

   the 
  Cycadeoidean 
  group, 
  have 
  been 
  described 
  from 
  European 
  

   localities, 
  chiefly 
  in 
  strata 
  of 
  Upper 
  Jurassic 
  or 
  questionably- 
  

   Lower 
  Cretaceous 
  age. 
  Recent 
  study 
  of 
  the 
  microscopic 
  features 
  

   of 
  the 
  American 
  forms 
  made 
  by 
  the 
  reviewer, 
  and 
  still 
  continued, 
  

   have 
  shown 
  their 
  close 
  parallelism 
  to 
  European 
  forms." 
  

  

  The 
  determination 
  of 
  this 
  highly 
  developed, 
  extensive, 
  and 
  

   probably 
  synchronous 
  development 
  of 
  cycadean 
  vegetation 
  on 
  

   both 
  continents 
  in 
  the 
  middle 
  Mesozoic 
  forms 
  one 
  of 
  the 
  most 
  

   interesting 
  additions 
  to 
  Paloeo-botanical 
  knowledge 
  made 
  in 
  

   recent 
  years. 
  g. 
  r. 
  w. 
  

  

  4, 
  Geologic 
  Atlets 
  of 
  the 
  United 
  States. 
  Telluride 
  Folio, 
  

   Colorado. 
  Areal 
  Geology 
  ; 
  by 
  Whitman 
  Cjeloss 
  assisted 
  by 
  

   Messrs. 
  Gane, 
  Lord 
  and 
  Spencer. 
  Topography, 
  by 
  Frank 
  

   Tweedy. 
  — 
  The 
  area 
  described 
  in 
  this 
  folio, 
  which 
  has 
  recently 
  

   become 
  so 
  well 
  known 
  from 
  its 
  valuable 
  gold 
  and 
  silver 
  mines, 
  is 
  

   situated 
  in 
  the 
  " 
  San 
  Juan 
  " 
  region. 
  The 
  chief 
  features 
  of 
  its 
  

   geology 
  are 
  the 
  Jura-Trias, 
  Cretaceous 
  strata 
  with 
  intrusions 
  of 
  

   igneous 
  rocks 
  in 
  the 
  form 
  of 
  stocks 
  and 
  laccoliths 
  and 
  the 
  great 
  

   outflows 
  of 
  rhyolite 
  and 
  piled 
  up 
  masses 
  of 
  rhyolitic 
  tuffs 
  and 
  

   breccias. 
  

  

  We 
  note 
  a 
  change 
  from 
  the 
  former 
  atlas 
  sheets 
  in 
  that 
  there 
  

   are 
  some 
  17 
  to 
  18 
  pages 
  of 
  text, 
  instead 
  of 
  the 
  usual 
  two 
  or 
  three. 
  

   With 
  the 
  large 
  page 
  this 
  gives 
  quite 
  a 
  full 
  treatment 
  of 
  the 
  

   geology 
  of 
  the 
  district, 
  equalling 
  perhaps 
  125 
  to 
  150 
  pages 
  of 
  an 
  

   ordinary 
  octavo 
  volume. 
  In 
  addition 
  there 
  are 
  three 
  half-tone 
  

   plates 
  of 
  beautiful 
  photographs 
  giving 
  eighteen 
  views 
  illustrating 
  

   thoroughly 
  the 
  topographic 
  features 
  and 
  broader 
  geologic 
  char- 
  

   acters 
  of 
  the 
  district. 
  We 
  trust 
  that 
  this 
  advance 
  in 
  the 
  scope 
  of 
  

   the 
  atlas 
  sheets 
  will 
  be 
  a 
  permanent 
  one, 
  especially 
  in 
  the 
  increase 
  

   of 
  the 
  descriptive 
  matter 
  in 
  the 
  text, 
  since 
  it 
  will 
  greatly 
  increase 
  

   the 
  value 
  of 
  the 
  work 
  as 
  a 
  whole 
  and 
  particularly 
  for 
  local 
  use. 
  

  

  In 
  addition 
  to 
  the 
  geology 
  by 
  Cross, 
  there 
  is 
  a 
  valuable 
  chapter 
  

   on 
  the 
  ore 
  deposits 
  by 
  C. 
  \V. 
  Purington, 
  treating 
  of 
  the 
  fissures, 
  

   veins, 
  etc. 
  l. 
  v. 
  r. 
  

  

  5. 
  The 
  Fresh/cater 
  Tertiary 
  Formations 
  of 
  the 
  llocky 
  Moun- 
  

   tain 
  Region 
  ; 
  by 
  W. 
  M. 
  Davis. 
  Proceedings 
  of 
  the 
  American 
  

   Academy 
  of 
  Science, 
  Vol. 
  xxxv, 
  No. 
  IV, 
  March, 
  1900. 
  — 
  The 
  lacus- 
  

   trine 
  origin 
  of 
  the 
  freshwater 
  Tertiary 
  deposits 
  of 
  our 
  western 
  

   states 
  was 
  asserted 
  by 
  nearly 
  all 
  of 
  the 
  early 
  workers 
  on 
  the 
  

   geological 
  surveys. 
  Hayden, 
  King, 
  Powell, 
  and 
  Dutton 
  describe 
  

   the 
  conditions 
  and 
  character 
  of 
  the 
  depositions 
  at 
  some 
  length, 
  

   and 
  their 
  conclusions 
  that 
  they 
  are 
  lake 
  sediments 
  are 
  supported 
  

  

  