﻿82 
  Scientific 
  Intelligence. 
  

  

  14. 
  Geology 
  and 
  Ore 
  Deposits 
  of 
  the 
  Monarch 
  and 
  Tomichi 
  

   Districts, 
  Colorado 
  ; 
  by 
  R. 
  D. 
  Crawford. 
  Pp. 
  317, 
  25 
  pis., 
  

   15 
  figs. 
  Bulletin 
  4, 
  Colorado 
  Geological 
  Survey, 
  1913. 
  — 
  The 
  

   area 
  described 
  in 
  this 
  bulletin 
  is 
  situated 
  in 
  the 
  southwestern 
  por- 
  

   tion 
  of 
  Chaffee 
  County 
  and 
  the 
  adjacent 
  southeastern 
  portion 
  of 
  

   Gunnison 
  County, 
  the 
  Monarch 
  District 
  lying 
  on 
  the 
  eastern 
  and 
  

   the 
  Tomichi 
  District 
  on 
  the 
  western 
  slope 
  of 
  the 
  Sawatch 
  Moun- 
  

   tain 
  Range. 
  The 
  region 
  is 
  one 
  of 
  high 
  relief, 
  ranging 
  from 
  an 
  

   altitude 
  of 
  6000 
  feet 
  to 
  the 
  summit 
  of 
  Shavano 
  Mountain, 
  14,239 
  

   feet. 
  The 
  pre-Cambrian 
  rocks 
  include 
  gneisses 
  and 
  schists 
  into 
  

   which 
  a 
  granite 
  batholith 
  is 
  intruded. 
  These 
  rocks 
  were 
  exposed 
  

   to 
  erosion 
  for 
  a 
  long 
  period 
  and 
  after 
  the 
  land 
  surface 
  was 
  

   reduced 
  to 
  almost 
  a 
  peneplain 
  there 
  followed 
  a 
  period 
  of 
  subsi- 
  

   dence 
  and 
  the 
  deposition 
  of 
  a 
  series 
  of 
  sedimentary 
  rocks. 
  Sedi- 
  

   mentation 
  was 
  interrupted 
  from 
  time 
  to 
  time 
  by 
  periods 
  of 
  

   elevation 
  and 
  erosion. 
  The 
  important 
  sedimentary 
  rocks 
  are 
  a 
  

   late 
  Cambrian 
  quartzite, 
  an 
  Ordovician 
  limestone, 
  a 
  parting 
  quartz- 
  

   ite, 
  an 
  Upper 
  Devonian 
  limestone, 
  a 
  black 
  dolomite 
  of 
  Missis- 
  

   sippian 
  time 
  and 
  Upper 
  Carboniferous 
  shales 
  and 
  sandstones. 
  

   Following 
  this 
  period 
  of 
  sedimentation 
  the 
  region 
  was 
  subjected 
  

   to 
  strong 
  compressive 
  forces 
  which 
  threw 
  the 
  strata 
  into 
  a 
  series 
  

   of 
  anticlines 
  and 
  synclines 
  and 
  developed 
  many 
  faults. 
  Probably 
  

   in 
  Tertiary 
  time 
  much 
  of 
  the 
  region 
  now 
  occupied 
  by 
  the 
  Sawatch 
  

   Range 
  was 
  invaded 
  by 
  a 
  huge 
  batholith 
  of 
  quartz 
  monzonite 
  

   whose 
  southern 
  limits 
  are 
  within 
  this 
  area. 
  This 
  intrusion 
  was 
  

   preceded 
  and 
  followed 
  by 
  intrusions 
  of 
  granular 
  rocks 
  in 
  stocks 
  

   and 
  by 
  minor 
  intrusions 
  of 
  porphyry. 
  

  

  The 
  ore 
  deposits 
  were 
  formed 
  probably 
  immediately 
  after 
  and 
  

   as 
  a 
  consequence 
  of 
  the 
  intrusion 
  of 
  the 
  quartz 
  monzonite. 
  The 
  

   first 
  discovery 
  of 
  ore 
  in 
  the 
  Monarch 
  District 
  was 
  in 
  1878. 
  The 
  

   various 
  mines 
  have 
  produced 
  since 
  then 
  approximately 
  $1 
  0,000,000 
  

   worth 
  of 
  ore. 
  The 
  deposits 
  are 
  of 
  various 
  types, 
  including: 
  (1) 
  

   Replacement 
  deposits 
  in 
  limestone, 
  (2) 
  filling 
  of 
  fault 
  fissures 
  in 
  

   the 
  sedimentary 
  rocks 
  with 
  replacement 
  of 
  the 
  wall 
  rocks, 
  (3) 
  

   fissure 
  veins 
  in 
  igneous 
  rocks. 
  (4) 
  contact 
  deposits. 
  The 
  greater 
  

   part 
  of 
  the 
  ores 
  have 
  been 
  silver-bearing 
  lead 
  carbonate. 
  Lead, 
  

   gold 
  and 
  zinc 
  have 
  also 
  been 
  produced. 
  The 
  Tomichi 
  District 
  

   was 
  discovered 
  in 
  1879. 
  Its 
  ores 
  have 
  produced 
  gold, 
  silver, 
  lead, 
  

   zinc, 
  copper 
  and 
  iron 
  in 
  commercial 
  quantity, 
  silver 
  and 
  lead 
  

   being, 
  however, 
  by 
  far 
  the 
  most 
  important. 
  w. 
  e. 
  f. 
  

  

  1 
  5. 
  The 
  Devonian 
  and 
  Mississippian 
  formations 
  of 
  northeastern 
  

   Ohio; 
  by 
  Charles 
  S. 
  Prosser. 
  Geological 
  Survey 
  of 
  Ohio, 
  J. 
  

   A. 
  Bownocker, 
  State 
  Geologist. 
  Fourth 
  series, 
  Bull. 
  15, 
  574 
  

   pp., 
  33 
  pis., 
  1 
  text 
  fig., 
  1912. 
  — 
  The 
  author 
  here 
  describes 
  in 
  great 
  

   detail 
  and 
  with 
  their 
  essential 
  fossils 
  the 
  many 
  sections 
  of 
  the 
  

   uppermost 
  Devonian 
  and 
  basal 
  Mississippian 
  formations 
  of 
  north- 
  

   eastern 
  Ohio 
  and 
  northwestern 
  Pennsylvania. 
  It 
  is 
  the 
  work 
  of 
  

   many 
  years, 
  done 
  between 
  professorial 
  duties. 
  The 
  writer 
  for 
  

   the 
  present 
  holds 
  that 
  the 
  black 
  shales 
  of 
  the 
  Huron, 
  Cleveland 
  

   and 
  Bedford, 
  when 
  traced 
  eastward 
  through 
  Ohio, 
  change 
  into 
  

  

  