﻿452 
  Scientific 
  Intelligence. 
  

  

  by 
  C. 
  R. 
  Van 
  Hise. 
  Monographs 
  of 
  the 
  U. 
  S. 
  Geol. 
  Survey, 
  vol. 
  

   XXXVI, 
  pp. 
  548, 
  4to 
  with 
  53 
  plates 
  and 
  maps.* 
  Washington, 
  

   1899. 
  — 
  The 
  report 
  and 
  the 
  accompanying 
  map 
  discussed 
  in 
  this 
  

   volume 
  cover 
  an 
  area 
  of 
  1296 
  sq. 
  miles, 
  including 
  the 
  Crystal 
  

   Falls, 
  the 
  Amasa, 
  the 
  Felch 
  Mountain 
  or 
  Metropolitan 
  and 
  the 
  

   Sturgeon 
  River 
  iron 
  ore 
  districts, 
  of 
  which 
  the 
  first 
  two 
  are 
  at 
  

   present 
  productive, 
  having 
  shipped 
  during 
  1898 
  a 
  total 
  of 
  325,814 
  

   tons. 
  The 
  Metropolitan 
  area 
  was 
  formerly 
  also 
  an 
  important 
  ore 
  

   producer 
  but 
  in 
  recent 
  years 
  the 
  mines 
  have 
  not 
  been 
  worked. 
  

   The 
  ores 
  are 
  mainly 
  non-Bessemer 
  hematites 
  and 
  limonites. 
  

  

  Geologically 
  the 
  district 
  may 
  be 
  regarded 
  as 
  connecting 
  the 
  

   Marquette 
  and 
  the 
  Menominee 
  districts. 
  It 
  consists 
  essentially 
  

   of 
  a 
  broad 
  area 
  of 
  Huronian 
  rocks 
  enclosing 
  two 
  small 
  oval 
  areas 
  

   of 
  Archean 
  schists 
  and 
  granites, 
  and 
  bordered 
  on 
  the 
  east 
  by 
  an 
  

   almost 
  continuous 
  stretch 
  of 
  similar 
  rocks. 
  The 
  Felch 
  Mountain 
  

   and 
  the 
  Sturgeon 
  River 
  areas 
  are 
  two 
  narrow 
  tongues 
  of 
  the 
  

   Huronian 
  sediments 
  extending 
  eastward 
  from 
  the 
  broad 
  expanse 
  

   of 
  the 
  Crystal 
  Falls 
  district 
  into 
  the 
  Archean 
  complex. 
  

  

  Structurally 
  the 
  main 
  portion 
  of 
  the 
  district 
  is 
  a 
  N.W.-S.E. 
  

   set 
  of 
  folds, 
  with 
  a 
  N.E.-S.W. 
  series 
  superinrposed 
  upon 
  them. 
  

   The 
  Felch 
  Mountain 
  and 
  Sturgeon 
  River 
  tongues 
  are 
  two 
  narrow 
  

   E.-W. 
  synclines. 
  

  

  In 
  structure 
  and 
  lithology 
  the 
  Archean 
  complex 
  possesses 
  no 
  

   unusual 
  features. 
  Its 
  rocks 
  are 
  biotite-granites 
  and 
  granite- 
  

   gneisses, 
  banded 
  gneisses, 
  mica-schists 
  and 
  hornblende 
  schists 
  or 
  

   amphibolites. 
  The 
  origin 
  of 
  the 
  mica-schists 
  and 
  the 
  banded 
  

   gneisses 
  is 
  not 
  known. 
  The 
  other 
  members 
  of 
  the 
  complex 
  are 
  

   plainly 
  igneous. 
  They 
  are 
  cut 
  by 
  numerous 
  basic 
  and 
  acid 
  dikes. 
  

  

  Between 
  the 
  Archean 
  and 
  the 
  Huronian 
  is 
  a 
  great 
  basal 
  con- 
  

   glomerate 
  best 
  exposed 
  in 
  the 
  Sturgeon 
  River 
  tongue. 
  Here 
  it 
  

   occurs 
  with 
  an 
  enormous 
  development. 
  It 
  is 
  a 
  schistose 
  recrys- 
  

   tallized 
  arkose 
  containing 
  many 
  large 
  pebbles 
  and 
  small 
  bowlders 
  

   of 
  granite, 
  gneiss 
  and 
  other 
  Archean 
  rocks. 
  Although 
  the 
  con- 
  

   glomerate 
  is 
  plainly 
  sedimentary, 
  it 
  has 
  suffered 
  such 
  deep-seated 
  

   metamorphism 
  that 
  specimens 
  of 
  its 
  finer 
  portions 
  can 
  with 
  diffi- 
  

   culty 
  be 
  distinguished 
  from 
  specimens 
  of 
  many 
  gneisses. 
  

  

  The 
  Huronian 
  Group 
  is 
  divided, 
  as 
  in 
  the 
  other 
  Lake 
  Superior 
  

   iron 
  districts, 
  into 
  a 
  lower 
  and 
  an 
  upper 
  division 
  separated 
  by 
  an 
  

   unconformity. 
  Though 
  definite 
  proof 
  of 
  this 
  unconformity 
  is 
  

   lacking 
  in 
  the- 
  Crystal 
  Falls 
  district, 
  there 
  is 
  little 
  doubt 
  that 
  it 
  

   exists, 
  since 
  the 
  strata 
  of 
  this 
  district 
  can 
  be 
  traced 
  almost 
  with- 
  

   out 
  break 
  into 
  the 
  neighboring 
  Marquette 
  district, 
  where 
  they 
  

   unquestionably 
  constitute 
  two 
  unconformable 
  series 
  of 
  formations. 
  

  

  In 
  the 
  eastern 
  part 
  of 
  the 
  district 
  the 
  Lower 
  Huronian 
  forma- 
  

   tions 
  are 
  better 
  represented 
  than 
  in 
  the 
  western 
  portion. 
  In 
  the 
  

  

  * 
  An 
  extract 
  of 
  this 
  monograph 
  appears 
  under 
  this 
  same 
  title 
  as 
  a 
  part 
  of 
  the 
  

   19th 
  Annual 
  Report 
  of 
  the 
  U. 
  S. 
  Geological 
  Survey 
  (Pt. 
  Ill, 
  pp. 
  1-151). 
  It 
  con- 
  

   tains 
  essentially 
  the 
  same 
  discussion 
  as 
  is 
  found 
  in 
  the 
  Monograph 
  with 
  the 
  excep- 
  

   tion 
  of 
  that 
  relating 
  to 
  the 
  microscopical 
  features 
  of 
  the 
  rocks 
  met 
  with 
  in 
  the 
  

   district. 
  

  

  