﻿402 
  PROF. 
  J. 
  D. 
  DANA 
  ON 
  THE 
  GEOLOGICAL 
  

  

  Brachiopods 
  of 
  the 
  genera 
  Orthis, 
  Strophomena 
  and 
  Rliynchonella, 
  

   species 
  of 
  OrtJioceras, 
  besides 
  the 
  Trilobate 
  Trinucleus 
  concentricus 
  

   " 
  in 
  great 
  abundance." 
  The 
  species 
  of 
  the 
  age 
  of 
  the 
  Chazy 
  lime- 
  

   stone 
  included 
  Pleurocystites 
  tenuiradiatus, 
  a 
  Pleurotomaria 
  near 
  

   P. 
  staminea 
  " 
  in 
  crowded 
  abundance," 
  Bathyurus 
  Angelini, 
  and 
  Asa- 
  

   phus 
  canalis. 
  Those 
  referred 
  to 
  the 
  Quebec 
  group 
  comprised 
  large 
  

   MaclurecB, 
  a 
  species 
  of 
  Rhynchonella 
  (some 
  beds 
  at 
  East 
  Cornwall 
  

   full 
  of 
  their 
  shells), 
  Bathyurus 
  Saffordi. 
  Those 
  of 
  the 
  Calciferous 
  

   beds 
  were 
  Ophileta 
  compacta, 
  0. 
  complanata, 
  Madurea 
  sordida, 
  

   M. 
  matutina, 
  small 
  species 
  of 
  OrtJioceras, 
  the 
  Trilobite 
  Bathyurus 
  

   amicus, 
  and 
  others. 
  

  

  As 
  these 
  species 
  of 
  the 
  Trenton 
  group 
  and 
  of 
  the 
  older 
  Chazy, 
  

   Quebec, 
  and 
  Calciferous 
  groups 
  were 
  collected 
  from 
  different 
  loca- 
  

   lities 
  in 
  one 
  and 
  the 
  same 
  limestone 
  mass 
  or 
  formation, 
  Mr. 
  Wing 
  

   arrived 
  at 
  the 
  very 
  natural 
  conclusion 
  that 
  (I 
  quote 
  his 
  own 
  words 
  

   from 
  a 
  letter 
  of 
  May, 
  1875): 
  — 
  " 
  The 
  Eolian 
  limestone 
  of 
  the 
  Ver- 
  

   mont 
  Geological 
  Report 
  embraced 
  not 
  only 
  the 
  Trenton 
  and 
  Hudson 
  - 
  

   river 
  beds, 
  but 
  all 
  the 
  formations 
  of 
  the 
  Lower 
  Silurian 
  as 
  well, 
  

   and 
  even 
  limestones 
  and 
  dolomites 
  of 
  the 
  Red-Sand-rock 
  [Potsdam 
  

   Sandstone] 
  series." 
  These 
  were 
  his 
  views 
  as 
  early 
  at 
  least 
  as 
  1872. 
  

   In 
  this 
  fact 
  the 
  limestone 
  is 
  like 
  that 
  of 
  the 
  Mississippi 
  basin 
  ; 
  for 
  

   there, 
  too, 
  a 
  single 
  limestone 
  formation, 
  with 
  but 
  small 
  inter- 
  

   ruptions, 
  covers 
  the 
  eras 
  of 
  the 
  Lower 
  Silurian 
  continuously 
  from 
  

   the 
  Calciferous 
  (if 
  not 
  the 
  Primordial) 
  to 
  the 
  Trenton 
  inclusive. 
  

  

  Thus 
  all 
  investigators 
  of 
  the 
  Taconic 
  belt 
  and 
  the 
  associated 
  

   rocks, 
  Professor 
  Emmons 
  included, 
  have 
  found 
  the 
  limestones 
  and 
  

   schists 
  one 
  in 
  stratification 
  and 
  one 
  in 
  system. 
  The 
  only 
  differences 
  

   are 
  these 
  : 
  — 
  

  

  Professor 
  Emmons 
  made 
  the 
  Taconic 
  schists 
  intermediate 
  in 
  age 
  

   between 
  the 
  two 
  limestones 
  and 
  the 
  western 
  limestone, 
  therefore 
  

   the 
  oldest, 
  because, 
  as 
  he 
  says, 
  this 
  was 
  the 
  order 
  of 
  superposition, 
  

   the 
  dip 
  of 
  the 
  whole 
  being 
  eastward. 
  Ho 
  states 
  on 
  page 
  147 
  of 
  his 
  

   Report 
  of 
  1842 
  : 
  — 
  " 
  So 
  long 
  as 
  the 
  more 
  western 
  belt 
  by 
  this 
  rule 
  

   is 
  the 
  inferior 
  limestone, 
  there 
  is 
  no 
  necessity 
  in 
  the 
  case 
  to 
  suppose 
  

   a 
  series 
  of 
  complicated 
  changes 
  in 
  order 
  to 
  make 
  it 
  coincide 
  with 
  

   conjectures." 
  

  

  Sir 
  William 
  Logan 
  was 
  led 
  by 
  his 
  studies 
  to 
  regard 
  the 
  schists 
  

   and 
  limestone 
  strata 
  as 
  together 
  of 
  the 
  Quebec 
  group. 
  

  

  The 
  Professors 
  Hitchcock 
  referred 
  the 
  rocks 
  to 
  the 
  Lower 
  Silu- 
  

   rian, 
  and 
  recognized 
  the 
  Taconic 
  schists 
  as 
  the 
  youngest 
  of 
  the 
  

   series. 
  

  

  Mr. 
  Wing 
  concluded 
  that 
  all 
  the 
  periods 
  of 
  the 
  Lower 
  Silurian 
  

   were 
  represented 
  in 
  the 
  limestone, 
  down 
  to 
  the 
  Primordial 
  and 
  up 
  

   to 
  the 
  Hudson-river 
  group, 
  and 
  that 
  the 
  Taconic 
  schists 
  were 
  the 
  

   youngest, 
  and 
  of 
  the 
  Hudson-river 
  group. 
  The 
  same 
  general 
  con- 
  

   clusion 
  was 
  adopted 
  theoretically 
  by 
  the 
  Professors 
  W. 
  B, 
  and 
  H* 
  

   D. 
  Rogers 
  in 
  1841, 
  and 
  by 
  Prof. 
  Mather 
  in 
  1843. 
  

  

  The 
  quartzitc 
  formation, 
  which 
  accompanies 
  the 
  eastern 
  lime- 
  

   stone 
  belt 
  in 
  Yermont, 
  Massachusetts, 
  and 
  Connecticut, 
  was 
  made 
  

   by 
  Prof. 
  Emmons 
  a 
  member 
  of 
  his 
  Taconic 
  system, 
  conformable 
  to 
  

  

  