﻿HUDSON 
  RIVER 
  BEDS 
  NEAR 
  ALBANY 
  565 
  

  

  the 
  writer 
  trusts, 
  have 
  been 
  secured 
  iu 
  sufficient 
  quantity 
  to 
  

   justify 
  a 
  reopening 
  of 
  the 
  discussion. 
  

  

  Both 
  investigators 
  based 
  their 
  defense 
  of 
  the 
  term 
  on 
  

   the 
  supposition 
  that 
  the 
  entire 
  series 
  of 
  the 
  Hudson 
  

   river 
  shales, 
  though 
  in 
  diminished 
  thickness, 
  continued 
  

   into 
  the 
  Mohawk 
  valley, 
  and 
  that 
  these, 
  like 
  the 
  Mohawk 
  

   valley 
  shales, 
  represented 
  only 
  the 
  lapse 
  of 
  time 
  be- 
  

   tween 
  the 
  Trenton 
  and 
  1 
  Medina 
  formations. 
  This 
  supposition, 
  

   though 
  at 
  that 
  time 
  warranted 
  by 
  the 
  facts 
  at 
  hand, 
  has 
  now 
  

   proved 
  to 
  be 
  only 
  partly 
  correct; 
  for 
  only 
  the 
  Utica 
  and 
  Lorraine 
  

   shales 
  of 
  the 
  Hudson 
  valley 
  continue 
  westward, 
  while 
  the 
  

   apparently 
  enormous 
  mass 
  of 
  Trenton 
  shales 
  does 
  not 
  leave 
  its 
  

   confines. 
  The 
  term 
  could 
  then 
  be 
  applied 
  only 
  to 
  the 
  shales 
  in 
  

   the 
  Hudson 
  valley 
  north 
  of 
  Cohoes 
  and 
  in 
  the 
  hills 
  on 
  the 
  west 
  

   side 
  of 
  the 
  valley 
  as 
  far 
  south 
  as 
  Albany, 
  while 
  the 
  shales 
  all 
  

  

  These 
  two 
  differential 
  features 
  of 
  the 
  Utica 
  faunas 
  of 
  the 
  Hudson 
  valley, 
  

   viz, 
  the 
  ascension 
  of 
  the 
  Trenton 
  forms 
  and 
  the 
  restriction 
  of 
  the 
  different 
  

   faunal 
  composition 
  to 
  the 
  marginal 
  region, 
  are 
  evidently 
  to 
  be 
  traced 
  to 
  the 
  

   same 
  cause. 
  The 
  assumption 
  that 
  these 
  Trenton 
  forms 
  continued 
  to 
  live 
  

   in 
  Utica 
  time 
  in 
  the 
  adjoining 
  Atlantic 
  basin, 
  while 
  they 
  had 
  become 
  

   extinct 
  on 
  the 
  American 
  continental 
  platform, 
  and 
  thus 
  were 
  enabled 
  to 
  

   leave 
  their 
  shells 
  in 
  the 
  deposits 
  of 
  the 
  eastern 
  continental 
  shelf, 
  seems 
  to 
  

   offer 
  a 
  reasonable 
  explanation. 
  

  

  At 
  the 
  same 
  time 
  it 
  is 
  evident 
  that 
  in 
  this 
  region 
  the 
  change 
  in 
  physical 
  

   conditions 
  from 
  the 
  Trenton 
  to 
  the 
  Utica 
  epoch 
  was 
  by 
  no 
  means 
  so 
  pro- 
  

   found 
  as 
  in 
  the 
  Mohawk 
  valley 
  and 
  west 
  of 
  it; 
  for 
  there 
  Utica 
  mud 
  shales 
  

   follow 
  more 
  or 
  less 
  pure 
  Trenton 
  limestones, 
  and 
  here 
  the 
  deposition 
  of 
  

   clastic 
  sediments 
  was 
  uninterrupted 
  from 
  the 
  lower 
  Trenton 
  to 
  the 
  top 
  of 
  

   the 
  Lorraine. 
  Such 
  forms 
  as 
  in 
  Trenton 
  time 
  were 
  accustomed 
  to 
  live 
  under 
  

   conditions 
  that 
  led 
  to 
  the 
  deposition 
  of 
  mud 
  and 
  sand 
  had 
  of 
  course 
  a 
  

   much 
  greater 
  chance 
  to 
  continue 
  living 
  when 
  the 
  Utica 
  time 
  was 
  ushered 
  

   in, 
  in 
  such 
  easy 
  stages 
  as 
  are 
  apparent 
  at 
  Mechanicsville 
  and 
  on 
  Green 
  

   Island, 
  than 
  the 
  faunas 
  farther 
  west. 
  But 
  it 
  is, 
  then, 
  pertinent 
  to 
  ask 
  

   why 
  these 
  forms 
  did 
  not 
  Wander 
  with 
  their 
  new 
  Utican 
  companions, 
  which 
  

   came 
  across 
  these 
  marginal 
  areas 
  on 
  the 
  continental 
  platform, 
  into 
  the 
  

   interior. 
  This 
  latter 
  fact 
  and 
  the 
  restriction 
  of 
  the 
  graptolite, 
  Coryn- 
  

   oides 
  curtus, 
  to 
  the 
  east 
  suggest 
  again 
  that 
  this 
  regional 
  difference 
  

   is 
  of 
  a 
  character 
  similar 
  to 
  that 
  between 
  the 
  Hudson 
  river 
  Trenton 
  and 
  

   the 
  continental 
  Trenton, 
  viz, 
  a 
  difference 
  between 
  the 
  oceanic 
  fauna, 
  

   encroaching 
  on 
  the 
  continental 
  margin, 
  and 
  the 
  fauna 
  of 
  a 
  shallow 
  con- 
  

   tinental 
  and 
  partially 
  inclosed 
  sea. 
  

  

  