﻿60 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  origin 
  of 
  their 
  beds 
  in 
  deeper 
  parts 
  of 
  the 
  sea 
  than 
  most 
  of 
  the 
  

   fossiliferous 
  rocks. 
  This 
  conception 
  is 
  found 
  to 
  be 
  in 
  full 
  accord 
  

   with 
  the 
  views 
  held 
  by 
  Suess, 
  Neumayr 
  and 
  Haug 
  in 
  regard 
  to 
  the 
  

   deeper 
  sea 
  origin 
  of 
  the 
  deposits 
  in 
  geosynclines 
  and 
  is 
  also 
  appli- 
  

   cable 
  to 
  the 
  Paleozoic 
  Appalachian 
  geosyncline, 
  as 
  far 
  as 
  the 
  Lower 
  

   Siluric 
  era 
  is 
  concerned. 
  The 
  graptolite 
  shales 
  of 
  the 
  Appalachian 
  

   geosyncline 
  reappear 
  in 
  Arkansas 
  and 
  the 
  Indian 
  Territory 
  and 
  

   again 
  in 
  the 
  Rocky 
  mountains, 
  but 
  are 
  absent 
  in 
  the 
  "vast 
  intervening 
  

   area. 
  These 
  facts 
  suggest 
  that 
  the 
  Appalachian 
  and 
  Rocky 
  moun- 
  

   tains 
  geosynclines 
  were 
  connected 
  in 
  the 
  south 
  by 
  a 
  westerly 
  bend 
  of 
  

   the 
  Appalachian 
  geosyncline 
  now 
  buried 
  in 
  the 
  Gulf 
  of 
  Mexico 
  or 
  

   the 
  Gulf 
  States, 
  a 
  northern 
  embayment 
  of 
  which 
  is, 
  however, 
  still 
  

   exposed 
  in 
  Arkansas 
  and 
  the 
  Indian 
  Territory. 
  

  

  A 
  synoptic 
  view 
  of 
  *the 
  genera 
  of 
  the 
  graptolites 
  of 
  the 
  United 
  

   States 
  is 
  given. 
  This 
  brings 
  out 
  graphically 
  the 
  fact 
  of 
  three 
  suc- 
  

   cessive 
  culminating 
  periods 
  of 
  the 
  graptolites, 
  each 
  marked 
  by 
  the 
  

   appearance 
  of 
  a 
  new 
  group 
  or 
  order 
  that 
  has 
  given 
  to 
  the 
  class 
  a 
  

   new 
  lease 
  of 
  life 
  by 
  advancing 
  to 
  a 
  new 
  structure. 
  The 
  first 
  of 
  these 
  

   is 
  the 
  dichograptid 
  culmination 
  in 
  the 
  Beekmantown 
  shale 
  ; 
  the 
  next 
  

   the 
  dicellograptid-diplograptid 
  climax 
  in 
  the 
  Trenton 
  shale 
  and 
  the 
  

   last 
  the 
  monograptid 
  culmination 
  in 
  the 
  Siluric. 
  The 
  structural 
  

   and 
  phylogenetic 
  causes 
  of 
  these 
  culminations 
  will 
  be 
  made 
  the 
  

   subject 
  of 
  a 
  separate 
  study. 
  

  

  A 
  separate 
  chapter 
  is 
  devoted 
  to 
  the 
  morphology 
  of 
  the 
  spines 
  

   of 
  the 
  graptolites 
  since 
  these 
  represent 
  one 
  of 
  the 
  striking 
  features 
  

   of 
  numerous 
  forms. 
  It 
  is 
  found 
  that 
  in 
  the 
  great 
  majority 
  of 
  forms 
  

   the 
  spines 
  are 
  placed 
  distinctly 
  on 
  the 
  most 
  exposed 
  parts 
  in 
  response 
  

   to 
  stimuli 
  from 
  the 
  environment. 
  In 
  many 
  others 
  (dwarfed 
  phylo- 
  

   genetic 
  forms) 
  a 
  general 
  spinosity 
  is 
  clearly 
  but 
  an 
  expression 
  of 
  

   waning 
  vital 
  power 
  and 
  in 
  a 
  third 
  important 
  group, 
  the 
  most 
  typical 
  

   representative 
  of 
  which 
  is 
  Glossograptus, 
  a 
  general 
  spinosity 
  is 
  

   •produced 
  by 
  a 
  tendency 
  to 
  repetition 
  of 
  the 
  lateral 
  spines 
  commonly 
  

   found 
  In 
  any 
  graptolite 
  at 
  the 
  sicular 
  extremity. 
  In 
  Lasiograptus 
  

   and 
  related 
  forms 
  finally 
  the 
  spines 
  were 
  found 
  to 
  result 
  from 
  the 
  

   suppression 
  of 
  thecal 
  structures 
  caused 
  by 
  restraint 
  of 
  environment, 
  

   or 
  in 
  an 
  endeavor 
  to 
  lighten 
  the 
  periderm. 
  

  

  Another 
  chapter 
  was 
  invited 
  by 
  the 
  multitude 
  of 
  forms 
  of 
  the 
  

   appendages 
  of 
  the 
  sicular 
  extremity 
  of 
  Climacograptus 
  

   b 
  i 
  c 
  o 
  r 
  n 
  i 
  s 
  occurring 
  in 
  the 
  Normanskill 
  shales. 
  It 
  was 
  found 
  that 
  

   the 
  several 
  varieties 
  based 
  on 
  the 
  forms 
  of 
  these 
  appendages 
  are 
  

   all 
  connected 
  by 
  transitions 
  and 
  represent 
  one 
  complex 
  system 
  mark- 
  

  

  