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  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  IV. 
  A 
  series 
  of 
  palaeozoic 
  sedimentary 
  rocks, 
  whose 
  oldest 
  

   member 
  is 
  the 
  Potsdam 
  sandstone 
  of 
  the 
  upper 
  Cambrian, 
  and 
  

   whose 
  latest 
  member 
  thus 
  far 
  identified 
  is 
  the 
  Utica 
  slate 
  of 
  the 
  

   Lower 
  Silurian 
  

  

  The 
  Potsdam 
  is 
  a 
  somewhat 
  calcareous 
  gray 
  quartzite, 
  some- 
  

   times 
  sparingly 
  provided 
  with 
  fos^ls. 
  it 
  often 
  shades 
  imper 
  

   ceptibly 
  into 
  the 
  Calciierous. 
  The 
  work 
  of 
  Brainerd 
  and 
  Seely 
  

   has 
  shown 
  the 
  Calciferous 
  to 
  be 
  of 
  unsuspected 
  thickness 
  It 
  

   involves 
  five 
  divisions, 
  all 
  of 
  which 
  are 
  displayed 
  near 
  old 
  Fort 
  

   Ticonderoga. 
  They 
  are 
  mostly 
  limestones, 
  involving 
  a 
  layer 
  

   of 
  fine-grained 
  sandstone 
  betwt 
  en 
  the 
  second 
  and 
  third. 
  ]STo 
  effort 
  

   has 
  been 
  made 
  to 
  subdivide 
  this 
  formation 
  in 
  our 
  work. 
  Above 
  

   the 
  Calciferous 
  lies 
  the 
  Chazy, 
  with 
  three 
  divisions, 
  according 
  to 
  

   the 
  same 
  authorities. 
  It 
  begins 
  with 
  a 
  thin, 
  slaty 
  sandstone 
  and 
  

   terminates 
  with 
  a 
  thin, 
  fine-grained 
  sandstone, 
  but 
  is 
  otherwise 
  

   limestone. 
  JSTo 
  attempt 
  to 
  subdivide 
  this 
  has 
  been 
  made. 
  Over 
  

   this 
  is 
  the 
  Trenton, 
  of 
  black 
  limestones, 
  both 
  well 
  bedded 
  and 
  

   shaly, 
  and 
  rich 
  in 
  fossils. 
  Still 
  higher, 
  the 
  Utica 
  slate 
  terminates 
  

   the 
  palaeozoic 
  series. 
  Our 
  stratigraphic 
  determinations 
  in 
  the 
  field 
  

   were 
  checked 
  by 
  identifications 
  of 
  the 
  fossils 
  by 
  Mr. 
  Gilbert 
  van 
  

   Ingen, 
  assistant 
  in 
  charge 
  of 
  the 
  geological 
  museum 
  at 
  Columbia 
  

   College, 
  who 
  made 
  a 
  trip 
  to 
  the 
  region, 
  at 
  my 
  request, 
  for 
  this 
  

   purpose. 
  All 
  these 
  sediments 
  are 
  conformable 
  and 
  were 
  depos- 
  

   ited 
  in 
  continuous 
  series. 
  They 
  have 
  suffered 
  minor 
  faulting 
  in 
  

   post-Ordovician 
  (Lower 
  Silurian) 
  time, 
  but 
  the 
  great 
  disturbances 
  

   that 
  have 
  chiefly 
  affected 
  the 
  first 
  three 
  series, 
  were 
  completed 
  

   before 
  their 
  deposition. 
  They 
  have 
  low 
  dips, 
  generally 
  to 
  the 
  

   north 
  or 
  northwest, 
  and 
  they 
  are 
  illustrated 
  in 
  their 
  relations 
  by 
  

   our 
  shore 
  sections. 
  Everything 
  indicates 
  that 
  their 
  inclined 
  con- 
  

   dition 
  is 
  a 
  remote 
  and 
  fading 
  result 
  of 
  the 
  upheaval 
  of 
  the 
  Green 
  

   mountains. 
  

  

  It 
  is 
  remarkable 
  that 
  we 
  do 
  not 
  find 
  some 
  trace 
  of 
  pre 
  Potsdam 
  

   strata, 
  which 
  are 
  so 
  abundant 
  in 
  Vermont, 
  but 
  none 
  have 
  yet 
  

   been 
  met. 
  

  

  Y. 
  A 
  subordinate 
  series 
  of 
  igneous 
  rocks 
  that 
  now 
  form 
  dikes 
  

   and 
  one 
  notable 
  laccolite, 
  and 
  that 
  are 
  later 
  than 
  the 
  Utica 
  slate. 
  

   These 
  consist 
  of 
  feldspar 
  porphyry, 
  which 
  is 
  best 
  developed 
  in 
  

   Essex 
  and 
  Willsborough, 
  and 
  of 
  basic 
  dikes 
  mostly 
  diabase 
  that 
  

   are 
  very 
  widespread 
  and 
  are 
  everywhere 
  met. 
  The 
  porphyries 
  

  

  