﻿Geology. 
  455 
  

  

  In 
  his 
  general 
  introduction 
  to 
  the 
  volume, 
  Van 
  Hise 
  calls 
  atten- 
  

   tion 
  to 
  the 
  fact 
  that 
  while 
  the 
  Hemlock 
  volcanics 
  were 
  being 
  

   erupted 
  in 
  one 
  portion 
  of 
  the 
  district 
  the 
  Mansfield 
  slates 
  and 
  the 
  

   Groveland 
  formation 
  were 
  being 
  laid 
  down 
  in 
  other 
  portions, 
  and 
  

   that 
  consequently 
  the 
  former 
  is 
  equivalent 
  in 
  part 
  of 
  the 
  district 
  

   to 
  the 
  last 
  two-named 
  formations 
  in 
  other 
  parts. 
  The 
  History 
  of 
  

   the 
  Crystal 
  Falls 
  district 
  closely 
  parallelizes 
  that 
  of 
  the 
  Marquette 
  

   district, 
  though 
  the 
  number 
  of 
  distinct 
  formations 
  recognized 
  in 
  it 
  

   is 
  smaller. 
  

  

  In 
  Chapter 
  ii 
  of 
  Part 
  II 
  of 
  the 
  volume, 
  Smyth 
  presents 
  an 
  

   interesting 
  discussion 
  of 
  the 
  use 
  of 
  magnetic 
  observations 
  in 
  

   mapping 
  the 
  distribution 
  of 
  magnetic 
  formations 
  and 
  working 
  out 
  

   their 
  structure. 
  The 
  chapter 
  is 
  an 
  abstract 
  of 
  a 
  paper 
  presented 
  

   at 
  the 
  Colorado 
  meeting 
  of 
  the 
  American 
  Institute 
  of 
  Mining 
  

   Engineers 
  in 
  September, 
  1896. 
  It 
  contains 
  many 
  points 
  of 
  great 
  

   value 
  to 
  field 
  geologists, 
  especially 
  to 
  those 
  who 
  are 
  engaged 
  in 
  

   the 
  study 
  of 
  iron-ore 
  regions, 
  and 
  it 
  is 
  extremely 
  interesting 
  from 
  

   a 
  theoretical 
  point 
  of 
  view. 
  

  

  It 
  is 
  unfortunate 
  that 
  the 
  authors 
  were 
  so 
  handicapped 
  in 
  their 
  

   work 
  by 
  the 
  lack 
  of 
  exposures, 
  since 
  some 
  of 
  their 
  conclusions, 
  to 
  

   one 
  unfamiliar 
  with 
  the 
  region, 
  appear 
  to 
  rest 
  on 
  insufficient 
  data. 
  

   But 
  when 
  we 
  remember 
  that 
  they 
  had 
  the 
  results 
  of 
  the 
  work 
  in 
  

   the 
  Penokee 
  and 
  the 
  Marquette 
  districts 
  to 
  guide 
  them 
  in 
  their 
  

   investigations, 
  it 
  would 
  seem 
  that 
  their 
  conclusions 
  must 
  in 
  the 
  

   main 
  be 
  correct. 
  They 
  have 
  at 
  least 
  shown 
  without 
  any 
  possi- 
  

   bility 
  of 
  question 
  that 
  in 
  the 
  Crystal 
  Falls 
  district 
  as 
  in 
  the 
  other 
  

   Lake 
  Superior 
  iron 
  districts, 
  the 
  ores 
  occur 
  in 
  Huronian 
  beds 
  

   which 
  are 
  unconformably 
  above 
  an 
  older 
  series 
  of 
  crystalline 
  

   schists, 
  and 
  that 
  the 
  ores 
  were 
  deposited 
  in 
  pitching 
  troughs 
  as 
  

   concentrates. 
  Glauconite 
  or 
  some 
  iron 
  carbonate 
  was 
  the 
  original 
  

   source 
  of 
  the 
  iron 
  and 
  descending 
  waters 
  were 
  the 
  agents 
  of 
  

   decomposition, 
  transportation 
  and 
  precipitation. 
  

  

  The 
  volume 
  is 
  well 
  illustrated 
  with 
  14 
  maps 
  and 
  plates 
  of 
  geo- 
  

   logical 
  sections 
  in 
  the 
  body 
  of 
  the 
  book, 
  two 
  maps 
  in 
  a 
  pocket, 
  

   37 
  other 
  plates, 
  of 
  which 
  27 
  are 
  microphotographs 
  and 
  24 
  figures 
  

   in 
  the 
  text. 
  

  

  4. 
  Preliminary 
  Report 
  on 
  the 
  Cape 
  Nome 
  Gold 
  region 
  in 
  

   Alaska; 
  by 
  F. 
  C. 
  Schkader 
  and 
  A. 
  H. 
  Brooks. 
  Pp. 
  56 
  with 
  

   maps 
  and 
  illustrations. 
  Washington, 
  1900 
  (U. 
  S. 
  Geological 
  

   Survey). 
  — 
  The 
  prompt 
  way 
  in 
  which 
  the 
  United 
  States 
  Geologi- 
  

   cal 
  Survey 
  comes 
  forward 
  with 
  scientific 
  information 
  in 
  regard 
  to 
  

   subjects 
  of 
  immediate 
  interest 
  to 
  the 
  public, 
  has 
  rarely 
  been 
  bet- 
  

   ter 
  shown 
  than 
  by 
  this 
  Report 
  on 
  the 
  Cape 
  Nome 
  Gold 
  Region, 
  

   which 
  is 
  based 
  upon 
  observations 
  made 
  by 
  Messrs. 
  Schrader 
  and 
  

   Brooks, 
  in 
  October, 
  1899. 
  It 
  states 
  that 
  the 
  bed-rock 
  of 
  the 
  

   Nome 
  district 
  consists 
  of 
  more 
  or 
  less 
  altered 
  limestones, 
  mica- 
  

   schists, 
  and 
  gneisses. 
  The 
  rocks 
  are 
  closely 
  folded 
  and 
  have 
  an 
  

   east-west 
  strike. 
  Mineralized 
  quartz 
  and 
  calcite 
  are 
  common. 
  

   The 
  gravels 
  are 
  classified 
  as 
  gulch, 
  terrace, 
  and 
  tundra 
  gravels, 
  

   those 
  of 
  the 
  beach 
  being 
  closely 
  related 
  to 
  the 
  latter. 
  The 
  

  

  