﻿92 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  This 
  black 
  basal 
  limestone 
  of 
  the 
  Trenton 
  contrasts 
  strongly 
  

   with 
  the 
  equally 
  thick 
  underlying 
  Seven 
  foot 
  tier 
  in 
  being 
  a 
  most 
  

   inconspicuous 
  element 
  in 
  the 
  physiography 
  of 
  the 
  region. 
  In 
  fact 
  

   its 
  presence 
  is 
  hardly 
  suspected 
  over 
  the 
  greater 
  part 
  of 
  the 
  area, 
  

   since 
  it 
  is 
  nearly 
  always 
  hidden 
  at 
  the 
  base 
  of 
  the 
  rounded 
  Trenton 
  

   hills. 
  Only 
  where 
  the 
  formations 
  are 
  planed 
  to 
  one 
  level, 
  as 
  about 
  

   Rosiere, 
  is 
  it 
  observed 
  to 
  outcrop 
  as 
  a 
  recognizable 
  belt. 
  

  

  The 
  remainder 
  of 
  the 
  Trenton, 
  as 
  far 
  as 
  the 
  area 
  of 
  the 
  map 
  is 
  

   concerned, 
  consists 
  then 
  of 
  about 
  50-60 
  feet 
  of 
  thin 
  slabby 
  lime- 
  

   stones, 
  with 
  shaly 
  intercalations. 
  The 
  limestones 
  are 
  partly 
  gray 
  

   and 
  crystalline 
  with 
  many 
  crinoid 
  joints 
  and 
  partly 
  fine 
  grained, 
  

   dark 
  gray 
  to 
  black. 
  The 
  latter 
  limestone 
  swells 
  sometimes 
  into 
  

   thicker 
  beds 
  (i 
  foot 
  thick 
  and 
  more) 
  of 
  black 
  limestone 
  which 
  is 
  

   either 
  quite 
  barren 
  of 
  fossils 
  save 
  worm 
  tubes, 
  or 
  as 
  on 
  Carleton 
  

   island, 
  almost 
  entirely 
  composed 
  of 
  the 
  shells 
  of 
  Plectambo- 
  

   nitessericeus. 
  

  

  Plate 
  25 
  shows 
  the 
  general 
  aspect 
  of 
  the 
  thin 
  bedded 
  limestones 
  

   in 
  the 
  creek 
  bed 
  at 
  Threemile 
  Bay 
  and 
  plate 
  24 
  which 
  gives 
  a 
  

   closer 
  view 
  of 
  the 
  rocks 
  in 
  the 
  same 
  locality, 
  illustrates 
  the 
  regular 
  

   alternations 
  of 
  limestones 
  and 
  shales 
  in 
  the 
  formation. 
  

  

  The 
  greater 
  middle 
  and 
  upper 
  part 
  of 
  the 
  Trenton 
  is 
  found 
  in 
  

   the 
  region 
  south 
  of 
  the 
  map, 
  on 
  the 
  other 
  side 
  of 
  Black 
  River 
  bay. 
  

  

  The 
  fauna 
  of 
  the 
  Trenton 
  has 
  the 
  general 
  aspect 
  of 
  that 
  of 
  the 
  

   formation 
  in 
  other 
  parts 
  of 
  the 
  State. 
  Its 
  details 
  have 
  not 
  yet 
  

   been 
  studied. 
  

  

  SUMMARY 
  OF 
  PALEOZOIC 
  OSCILLATIONS 
  OF 
  LEVELi 
  

  

  It 
  has 
  been 
  shown 
  that 
  the 
  Potsdam 
  and 
  Theresa 
  formations 
  were 
  

   deposited 
  in 
  the 
  west 
  end 
  of 
  a 
  sagging 
  basin 
  or 
  trough 
  which 
  occu- 
  

   pied 
  the 
  general 
  line 
  of 
  the 
  present 
  St 
  Lawrence 
  valley; 
  that 
  the 
  

   deposition 
  began 
  at 
  the 
  east 
  and 
  worked 
  westward, 
  involving 
  our 
  

   region 
  here 
  only 
  in 
  its 
  later 
  stage 
  ; 
  and 
  that 
  the 
  depressed 
  trough 
  was 
  

   a 
  westward 
  extension 
  from 
  a 
  similar 
  subsiding 
  trough 
  along 
  the 
  

   Champlain 
  valley 
  line. 
  There 
  the 
  Potsdam 
  is 
  very 
  thick, 
  is 
  followed 
  

   by 
  beds 
  similar 
  to 
  those 
  here 
  called 
  Theresa, 
  and 
  these 
  are 
  overlaid 
  

   by 
  nearly 
  400 
  feet 
  of 
  dolomites 
  which 
  have 
  been 
  heretofore 
  classed 
  

   with 
  the 
  Beekmantown 
  formation, 
  as 
  Division 
  A 
  of 
  that 
  formation. 
  

   No 
  such 
  beds 
  as 
  these 
  last 
  appear 
  in 
  our 
  district 
  here, 
  though 
  the 
  

   Potsdam 
  and 
  Theresa 
  may 
  be 
  equivalent 
  to 
  them 
  in 
  time. 
  In 
  the 
  

   Champlain 
  valley 
  also 
  appear 
  four 
  other 
  divisions 
  of 
  the 
  Beekman- 
  

   town, 
  with 
  an 
  aggregate 
  thickness 
  in 
  the 
  neighborhood 
  of 
  1400 
  feet. 
  

  

  1 
  By 
  H. 
  P. 
  dishing. 
  

  

  