﻿HUDSON 
  RIVER 
  BEDS 
  NEAR 
  ALBANY 
  561 
  

  

  tion 
  as 
  a 
  whole 
  dwindled 
  to 
  an 
  insignificant 
  thickness, 
  or 
  

   that 
  only 
  a 
  short 
  span 
  of 
  the 
  Trenton 
  period 
  is 
  represented 
  in 
  the 
  

   lower 
  Mohawk 
  valley 
  by 
  limestone, 
  presumably 
  the 
  earliest 
  por- 
  

   tion, 
  as 
  in 
  the 
  Hudson 
  valley. 
  The 
  facts 
  at 
  hand 
  do 
  not 
  permit 
  

   a 
  choice 
  between 
  the 
  two 
  alternatives, 
  but 
  the 
  thinning 
  out 
  of 
  the 
  

   limestone, 
  together 
  with 
  the 
  entire 
  absence 
  of 
  the 
  Dicellograptus 
  

   fauna 
  in 
  the 
  Mohawk 
  valley, 
  suggests 
  the 
  presence 
  of 
  a 
  barrier, 
  

   perhaps 
  by 
  a 
  shallowing 
  of 
  the 
  sea 
  as 
  indicated 
  by 
  the 
  thin 
  forma- 
  

   tion 
  of 
  limestone 
  in 
  the 
  region 
  of 
  the 
  lower 
  Mohawk, 
  in 
  early 
  

   Trenton 
  time. 
  The 
  very 
  peculiar 
  Trenton 
  fauna 
  of 
  the 
  limestone 
  

   conglomerate 
  of 
  Rysedorph 
  hill 
  and 
  Moordener 
  kill, 
  characterized 
  

   by 
  the 
  occurrence 
  of 
  Plectambonites 
  sericea 
  var. 
  

   aspera, 
  Plectambonites 
  aff. 
  gibbosa, 
  Chris- 
  

   tiania, 
  Eccyliopterus, 
  Ampyx 
  and 
  Remopleu- 
  

   rides, 
  indicates 
  a 
  great 
  faunistic 
  difference 
  between 
  the 
  Hud- 
  

   son 
  valley 
  and 
  Mohawk 
  valley 
  regions 
  even 
  before 
  the 
  deposition 
  

   of 
  the 
  Dicellograptus 
  zone, 
  and 
  at 
  the 
  time 
  of 
  the 
  deposition 
  of 
  

   the 
  basal 
  Trenton 
  limestone 
  beds. 
  

  

  DISCONTINUITY 
  OF 
  FAUNISTIC 
  SUCCESSION 
  IN 
  TREN- 
  

   TON 
  AND 
  UTICA 
  BEDS 
  

  

  A 
  fact 
  apparently 
  incongruous 
  with 
  the 
  separation 
  of 
  the 
  Nor- 
  

   mans 
  kill 
  and 
  the 
  Utica 
  shales 
  by 
  the 
  middle 
  and 
  upper 
  Trenton 
  

   beds 
  is 
  the 
  discontinuity 
  of 
  the 
  faunistic 
  succession 
  in 
  these 
  Tren- 
  

   ton 
  beds; 
  for, 
  while 
  the 
  lower 
  Dicellograptus 
  fauna 
  disappears 
  

   in 
  the 
  middle 
  Trenton 
  shales, 
  a 
  small 
  part 
  of 
  the 
  graptolite 
  fauna 
  

   of 
  the 
  Dicellograptus 
  zone 
  reappears 
  in 
  the 
  Utica 
  shale. 
  It 
  is 
  

   this 
  observation 
  which 
  induced 
  Whitfield 
  and 
  Walcott 
  to 
  connect 
  

   the 
  Normans 
  kill 
  with 
  the 
  Utica 
  shale. 
  On 
  the 
  other 
  hand, 
  the 
  

   graptolite, 
  Diplograptus 
  amplexicaulis, 
  common 
  

   in 
  the 
  middle 
  Trenton, 
  disappears 
  in 
  the 
  Utica 
  shale 
  and 
  is 
  said 
  

   to 
  reappear 
  in 
  the 
  Lorraine 
  beds. 
  The 
  latter 
  fact 
  is 
  in 
  accordance 
  

   with 
  the 
  known 
  return 
  of 
  other 
  Trenton 
  forms 
  in 
  Lorraine 
  times. 
  

   The 
  explanation 
  of 
  this 
  alternating 
  recession 
  and 
  return 
  of 
  grap- 
  

   tolite 
  faunas 
  in 
  the 
  Hudson 
  valley 
  region 
  seems 
  to 
  lie 
  in 
  the 
  dis- 
  

   tribution 
  of 
  the 
  faunas 
  and 
  the 
  character 
  of 
  the 
  associate 
  forms. 
  

  

  