﻿20 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  relative 
  value 
  of 
  the 
  mines 
  in 
  which 
  they 
  occar 
  as 
  ores. 
  Apart 
  from 
  

   this 
  more 
  practical 
  consideration, 
  the 
  data 
  collected 
  are 
  an 
  addition 
  to 
  

   mineralogical 
  science. 
  Comparatively 
  little 
  is 
  known 
  thus 
  far 
  re- 
  

   garding 
  the 
  distribution 
  of 
  minerals 
  throughout 
  the 
  earth, 
  and 
  every 
  

   additional 
  catalogue, 
  if 
  conscientiously 
  prepared, 
  giving 
  sufficient 
  details, 
  

   is 
  a 
  contribution 
  to 
  science, 
  — 
  a 
  contribution 
  which, 
  from 
  its 
  character, 
  

   may, 
  when 
  the 
  collection 
  of 
  facts 
  is 
  complete 
  enough, 
  lead 
  to 
  important 
  

   and 
  valuable 
  generalizations. 
  

  

  Every 
  attentive 
  reader 
  must 
  have 
  noticed 
  that 
  there 
  is, 
  and 
  has 
  been 
  

   of 
  late 
  years, 
  considerable 
  difference 
  of 
  opinion 
  among 
  geologists 
  and 
  

   palaeontologists, 
  each 
  eminent 
  in 
  his 
  own 
  department, 
  as 
  to 
  the 
  true 
  geo- 
  

   logical 
  age 
  of 
  several 
  of 
  the 
  formations 
  hitherto 
  studied 
  in 
  the 
  Western 
  

   Territories. 
  This 
  difference 
  of 
  opinion 
  does 
  not 
  arise 
  from 
  any 
  failure 
  

   of 
  each 
  to 
  understand 
  his 
  own 
  facts 
  correctly, 
  but 
  because 
  American 
  

   scientists 
  have 
  heretofore 
  been 
  content 
  to 
  use 
  a 
  foreign 
  standard, 
  believ- 
  

   ing 
  that 
  it 
  was 
  inflexibly 
  applicable 
  to 
  the 
  whole 
  world. 
  Accumulated 
  

   experience 
  has 
  shown 
  that 
  the 
  various 
  evolutional 
  tides 
  of 
  organic 
  life 
  

   have 
  not 
  advanced 
  at 
  the 
  same 
  rate 
  in 
  all 
  parts 
  of 
  the 
  world. 
  Thus, 
  

   while 
  we 
  find 
  that 
  a 
  certain 
  grade 
  of 
  vertebrates, 
  invertebrates, 
  and 
  

   plants 
  are 
  associated 
  together 
  in 
  the 
  strata 
  of, 
  and 
  collectively 
  charac- 
  

   terize, 
  a 
  certain 
  geological 
  period 
  in 
  Europe, 
  in 
  America 
  we 
  find 
  that 
  

   the 
  same 
  grade 
  of 
  plant 
  life 
  was 
  evidently 
  reached 
  much 
  earlier, 
  and 
  the 
  

   same 
  grade 
  of 
  vertebrate 
  life 
  was 
  continued 
  much 
  later, 
  etc. 
  In 
  short, 
  

   using 
  the 
  European 
  standard, 
  we 
  find 
  in 
  America 
  an 
  actual 
  mingling 
  

   in 
  the 
  same 
  strata 
  of 
  Cretaceous 
  and 
  Tertiary 
  types 
  of 
  organic 
  remains. 
  

   From 
  the 
  fact 
  that 
  all 
  fossiliferous 
  strata 
  are 
  sedimentary 
  accumulations 
  

   in 
  seas 
  or 
  other 
  bodies 
  of 
  water, 
  the 
  remains 
  of 
  invertebrate 
  animals 
  are 
  

   far 
  more 
  abundant 
  than 
  any 
  other, 
  because 
  they 
  lived 
  in 
  and 
  upon 
  the 
  

   sediment 
  while 
  it 
  was 
  accumulating, 
  winle 
  the 
  remains 
  of 
  land 
  animals 
  

   and 
  plants 
  could 
  have 
  reached 
  the 
  places 
  of 
  their 
  entombment 
  only 
  from 
  

   the 
  shores. 
  Thus, 
  invertebrate 
  fossils 
  have 
  always 
  been 
  regarded 
  as, 
  

   more 
  reliable 
  and 
  valuable 
  than 
  any 
  other 
  in 
  determining 
  the 
  geologica' 
  

   age 
  of 
  the 
  strata 
  containing 
  them. 
  Indeed, 
  they 
  have 
  generally 
  bee 
  

   regarded, 
  as 
  they 
  often 
  are, 
  the 
  only 
  available 
  evidence, 
  and 
  entire! 
  

   sufficient. 
  It 
  was 
  with 
  this 
  generally 
  accepted 
  invertebrate 
  standard 
  

   in 
  mind, 
  that 
  all 
  the 
  early 
  explorers 
  of 
  the 
  geology 
  of 
  the 
  Western 
  Terri- 
  

   tories 
  referred 
  the 
  various 
  groups 
  of 
  strata 
  they 
  found 
  to 
  the 
  different 
  

   geological 
  periods, 
  and 
  the 
  differences 
  of 
  opinion 
  have 
  arisen 
  through 
  

   subsequent 
  investigations 
  of 
  the 
  fossil 
  plants 
  and 
  vertebrates 
  of 
  the 
  

   same 
  groups. 
  The 
  result 
  of 
  all 
  this 
  is 
  not 
  confusion, 
  but 
  beautiful 
  har- 
  

   mony. 
  It 
  shows 
  that 
  we 
  have 
  in 
  Western 
  IsTorth 
  America 
  an 
  unbroken 
  

   series 
  of 
  strata, 
  ranging 
  from 
  early 
  and 
  unmistakable 
  Cretaceous 
  folate 
  

   and 
  equally 
  unmistakable 
  Tertiary. 
  There 
  are 
  consequently 
  several 
  

   groups 
  of 
  strata, 
  transitional 
  in 
  their 
  character, 
  that 
  different 
  special- 
  

   ists, 
  viewing 
  their 
  fossil 
  contents 
  from 
  different 
  standpoints, 
  are 
  dis- 
  

   posed 
  to 
  place 
  a 
  little 
  higher 
  or 
  lower 
  in 
  the 
  geological 
  scale, 
  as 
  the 
  case 
  

  

  