﻿348 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  The 
  more 
  interesting 
  features 
  in 
  this 
  succession 
  of 
  the 
  faunas 
  

   are. 
  somewhat 
  obscured 
  and 
  too 
  briefly 
  expressed 
  in 
  such 
  a 
  

   tabulation 
  as 
  the 
  foregoing. 
  

  

  Following 
  the 
  sequence 
  in 
  its 
  natural 
  order 
  from 
  beneath 
  

   upward, 
  the 
  first 
  fossil 
  encountered 
  in 
  the 
  great 
  thickness 
  of 
  

   hydraulic 
  limestone 
  overlying 
  the 
  salt, 
  is 
  a 
  large 
  sized 
  Leperditia 
  

   like 
  L. 
  alta 
  and 
  L. 
  Jonesi 
  in 
  size 
  and 
  form 
  and 
  also 
  resembling 
  

   the 
  species 
  occurring 
  in 
  the 
  Coralline 
  limestone 
  at 
  Schoharie 
  

   which 
  was 
  originally 
  identified 
  as 
  L. 
  alta. 
  It 
  would 
  perhaps 
  be 
  

   difficult 
  to 
  say 
  whether 
  this 
  is 
  actually 
  the 
  characteristic 
  species 
  

   of 
  the 
  Tentaculite 
  limestone 
  (Z. 
  alta) 
  appearing 
  so 
  early, 
  or, 
  if 
  

   this 
  is 
  the 
  case, 
  whether 
  the 
  same 
  species 
  has 
  not 
  maintained 
  an 
  

   unmodified 
  existence 
  from 
  the 
  late 
  faunas 
  of 
  the 
  Niagara 
  period. 
  

   Our 
  specimens 
  being 
  in 
  the 
  form 
  of 
  casts 
  do 
  not 
  permit 
  the 
  

   determination 
  of 
  so 
  nice 
  a 
  point. 
  The 
  favosite 
  occurring 
  at 
  

   10^5' 
  also 
  determines 
  nothing, 
  but 
  from 
  above 
  this 
  point 
  where 
  

   the 
  lithological 
  character 
  of 
  the 
  rock 
  changes 
  noticeably, 
  to 
  

   1010' 
  we 
  have 
  a 
  well- 
  developed 
  Tentaculite 
  limestone 
  fauna. 
  

  

  It 
  is 
  a 
  noteworthy 
  fact 
  and 
  one 
  that 
  has 
  been 
  frequently 
  

   adverted 
  to, 
  that 
  the 
  Lower 
  Helderberg 
  series 
  of 
  strata 
  loses 
  

   its 
  differentiation 
  westward 
  in 
  New 
  York 
  beyond 
  the 
  region 
  

   of 
  its 
  typical 
  exposure; 
  and 
  the 
  faunas 
  of 
  these 
  separate 
  

   divisions 
  also 
  lose 
  their 
  individuality. 
  With 
  the 
  thinning 
  of 
  the 
  

   formation 
  to 
  the 
  west 
  the 
  faunas 
  become 
  commingled, 
  more 
  

   and 
  more 
  sparse, 
  with 
  a 
  notable 
  prevalence 
  of 
  that 
  of 
  the 
  

   Tentaculite 
  limestone, 
  the 
  basal 
  member 
  of 
  the 
  series, 
  until 
  

   finally, 
  as 
  shown 
  in 
  the 
  Livonia 
  section, 
  the 
  entire 
  group 
  is 
  repre- 
  

   sented 
  by 
  a 
  thickness 
  of 
  about 
  thirty 
  -five 
  feet 
  containing 
  a 
  fauna 
  

   wholly 
  composed 
  of 
  Tentaculite 
  limestone 
  species. 
  

  

  The 
  nearest 
  point 
  to 
  the 
  eastward 
  of 
  the 
  Livonia 
  meridian 
  

   where 
  a 
  good 
  exposure 
  of 
  the 
  Lower 
  Helderberg 
  rocks 
  has 
  been 
  

   carefully 
  studied 
  is 
  near 
  Union 
  Springs 
  in 
  Cayuga 
  county, 
  at 
  

   which 
  place 
  Prof. 
  Williams 
  has 
  shown* 
  the 
  presence 
  of 
  a 
  con- 
  

   siderable 
  element 
  from 
  the 
  upper 
  faunas 
  of 
  the 
  Lower 
  Helder- 
  

   berg 
  group, 
  represented 
  by 
  such 
  species 
  as 
  Orthostrophia 
  stropho- 
  

   menoides, 
  Nucleospira 
  ventricosa, 
  etc. 
  

  

  * 
  American 
  Journal 
  of 
  Science, 
  September, 
  1685, 
  and 
  February, 
  1886; 
  Report 
  of 
  New 
  York 
  

   State 
  G 
  logist 
  for 
  1886, 
  p. 
  10. 
  

  

  