﻿384 
  Scientific 
  Intelligence. 
  

  

  dikes 
  — 
  22 
  of 
  which 
  are 
  mapped. 
  The 
  remaining 
  geological 
  his- 
  

   tory 
  is 
  concerned 
  with 
  the 
  events 
  which 
  transpired 
  in 
  the 
  Glacial, 
  

   Champlain 
  and 
  Recent 
  periods. 
  h. 
  e. 
  g. 
  

  

  2. 
  A 
  Contribution 
  to 
  the 
  Geology 
  of 
  'the 
  Northern 
  Black 
  Hills 
  ; 
  

   by 
  John 
  Duer 
  Irving. 
  Annals 
  New 
  York 
  Academy 
  of 
  Sciences, 
  

   Vol. 
  xii, 
  No. 
  9, 
  pp. 
  187-340, 
  Pis. 
  v-xvi, 
  figs. 
  5-20.— 
  This 
  paper 
  

   is 
  for 
  the 
  most 
  part 
  a 
  detailed 
  petrographical 
  study 
  of 
  an 
  area 
  

   just 
  west 
  of 
  Deadwood, 
  So. 
  Dakota, 
  which 
  is 
  important 
  because 
  

   of 
  its 
  interesting 
  rock 
  types 
  and 
  intrusions, 
  and 
  also 
  as 
  the 
  home 
  

   of 
  an 
  increasing 
  mining 
  industry. 
  The 
  first 
  few 
  pages 
  of 
  the 
  

   report 
  are 
  devoted 
  by 
  Dr. 
  Irving 
  to 
  a 
  description 
  of 
  the 
  Algon- 
  

   kian, 
  Cambro-Silurian 
  and 
  Carboniferous 
  strata, 
  after 
  which 
  the 
  

   eruptives 
  which 
  occur 
  here 
  in 
  great 
  variety 
  are 
  discussed. 
  The 
  

   position 
  of 
  the 
  intrusions 
  indicates 
  that 
  the 
  Black 
  Hills 
  were 
  

   twice 
  subjected 
  to 
  prolonged 
  igneous 
  disturbances 
  ; 
  once 
  previous 
  

   to 
  the 
  metamorphism 
  of 
  the 
  Algonkian 
  when 
  the 
  intrusions 
  were 
  

   basic 
  (amphibolites) 
  ; 
  and 
  again 
  during 
  Post-Cretaceous 
  times 
  

   after 
  the 
  Paleozoic 
  and 
  Mesozoic 
  sediments 
  had 
  been 
  deposited. 
  

   These 
  later 
  intrusives 
  are 
  alkaline 
  and 
  have 
  no 
  genetic 
  relation- 
  

   ship 
  with 
  the 
  amphibolites. 
  In 
  considering 
  the 
  form 
  assumed 
  by 
  

   the 
  intrusions, 
  the 
  author 
  differs 
  somewhat 
  from 
  Newton, 
  Russell, 
  

   and 
  other 
  workers 
  in 
  this 
  region. 
  He 
  concludes 
  ' 
  that 
  the 
  influ- 
  

   ence 
  of 
  the 
  rocks 
  into 
  whi,eh 
  the 
  magmas 
  are 
  intruded 
  has 
  been 
  

   the 
  determining 
  factor 
  of 
  the 
  form 
  assumed 
  by 
  the 
  intrusion' 
  (p. 
  

   244). 
  

  

  Petrographical 
  examination 
  of 
  the 
  rocks 
  shows 
  eight 
  families, 
  

   as 
  follows 
  : 
  grorudite, 
  phonolite, 
  rhyolite, 
  andesite, 
  dacite, 
  diorite, 
  

   lamprophyre, 
  amphibolites. 
  Phonolite 
  occurs 
  most 
  abundantly 
  

   and 
  is 
  described 
  at 
  considerable 
  length. 
  

  

  The 
  ore 
  bodies 
  of 
  the 
  region 
  are 
  found 
  in 
  three 
  geological 
  

   ages 
  — 
  Algonkian, 
  Cambrian 
  and 
  Carboniferous. 
  The 
  Algonkian 
  

   ores 
  occur 
  as 
  impregnated 
  zones 
  in 
  the 
  metamorphosed 
  slates 
  and 
  

   schists, 
  like 
  the 
  Homestake 
  mine 
  at 
  Lead 
  City. 
  The 
  Cambrian 
  

   areas 
  which 
  for 
  the 
  last 
  few 
  years 
  have 
  yielded 
  the 
  greatest 
  out- 
  

   put 
  of 
  all 
  the 
  Black 
  Hills 
  Mines 
  are 
  replacements 
  of 
  impure 
  lime- 
  

   stones 
  by 
  siliceous 
  solutions 
  bearing 
  gold. 
  The 
  Carboniferous 
  

   ores 
  which 
  have 
  not 
  as 
  yet 
  been 
  fully 
  exploited 
  are 
  silicified 
  

   brecciated 
  limestone, 
  much 
  like 
  the 
  Cambrian 
  deposits. 
  Numerous 
  

   diagrams, 
  sections 
  and 
  photographs 
  increase 
  the 
  usefulness 
  of 
  the 
  

   work. 
  h. 
  e. 
  g. 
  

  

  3. 
  Description 
  of 
  a 
  New 
  Genus 
  and 
  Twenty 
  New 
  Species 
  of 
  

   Fossil 
  Cycadean 
  Trunks 
  from 
  the 
  Jurassic 
  of 
  Wyoming 
  • 
  by 
  

   Lester 
  F. 
  Ward. 
  Proceedings 
  of 
  the 
  Washington 
  Academy 
  of 
  

   Sciences, 
  vol. 
  i, 
  pp. 
  253-300 
  (PI. 
  xiv-xxi), 
  Feb. 
  14, 
  1900. 
  — 
  In 
  

   this 
  contribution 
  Professor 
  Ward 
  adds 
  another 
  important 
  chap- 
  

   ter 
  to 
  our 
  knowledge 
  of 
  the 
  cycadean 
  vegetation 
  of 
  the 
  North 
  

   American 
  Mesozoic. 
  

  

  The 
  determination 
  of 
  the 
  new 
  genus 
  and 
  species 
  is 
  the 
  result 
  

   of 
  a 
  study 
  of 
  85 
  specimens 
  from 
  Carbon 
  County, 
  Wyoming. 
  Of 
  

   the 
  types, 
  two, 
  Gycadella 
  Beecheriana 
  and 
  Cycadella 
  Reedii 
  

  

  