﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  55 
  

  

  their 
  own. 
  Fossil 
  seaweeds,, 
  but 
  not 
  animal 
  remains, 
  are 
  common 
  

   in 
  the 
  Onei 
  da-Medina 
  beds. 
  Various 
  fossils 
  exist 
  in 
  profusion 
  in 
  

   the 
  Clinton 
  and 
  Niagara 
  formations, 
  while 
  in 
  the 
  middle 
  Salina 
  

   beds 
  fossils 
  are 
  altogether 
  absent 
  because 
  the 
  water 
  of 
  that 
  time 
  

   was 
  intensely 
  saline. 
  The 
  waterlime 
  beds 
  at 
  the 
  base 
  and 
  top 
  of 
  

   the 
  Salina 
  are 
  usually 
  poor 
  in 
  fossils 
  except 
  for 
  the 
  remarkable 
  

   assemblage 
  of 
  organic 
  remains 
  known 
  as 
  eurypterids 
  which 
  be- 
  

   longed 
  to 
  the 
  arachnid 
  class 
  but 
  are 
  now 
  wholly 
  extinct. 
  Fossils 
  

   are 
  generally 
  rather 
  common 
  in 
  the 
  uppermost 
  Siluric 
  beds 
  of 
  the 
  

   State. 
  

  

  DEVONIC 
  AND 
  CARBONIC 
  PERIODS 
  

  

  The 
  Devonic 
  history 
  of 
  New 
  York 
  State 
  is 
  comparatively 
  simple 
  

   and 
  the 
  records 
  are 
  remarkably 
  well 
  shown 
  in 
  rocks 
  of 
  that 
  age. 
  

   Devonic 
  strata 
  comprise 
  the 
  zvhole 
  Catdkill 
  and 
  Southzve 
  stern 
  

   plateau 
  provinces, 
  except 
  for 
  a 
  fezv 
  small 
  patches 
  of 
  Carbonic 
  rocks, 
  

   and 
  thus 
  cover 
  more 
  than 
  one-third 
  of 
  the 
  area 
  of 
  the 
  State. 
  They 
  

   are 
  more 
  widespread 
  on 
  the 
  surface 
  than 
  the 
  rocks 
  of 
  any 
  other 
  age. 
  

   The 
  combined 
  thickness 
  of 
  the 
  Devonic 
  strata 
  is 
  over 
  4000 
  feet, 
  

   which 
  is 
  considerably 
  more 
  than 
  for 
  any 
  other 
  Paleozoic 
  period 
  in 
  

   the 
  State. 
  

  

  That 
  the 
  Devonic 
  strata, 
  on 
  the 
  Hudson 
  valley 
  side, 
  formerly 
  

   extended 
  some 
  miles 
  farther 
  eastward 
  than 
  they 
  now 
  do 
  is 
  proved 
  

   by 
  the 
  presence 
  of 
  small 
  outliers 
  of 
  Devonic 
  rock, 
  for 
  example, 
  

   Becraft 
  mountain 
  just 
  southeast 
  of 
  Hudson, 
  the 
  Rensselaer 
  grit 
  

   farther 
  north 
  and 
  the 
  Skunnemunk 
  mountain 
  southwest 
  of 
  New- 
  

   burgh. 
  During 
  part 
  of 
  the 
  time 
  the 
  Devonic 
  sea, 
  or 
  arms 
  of 
  it, 
  

   reached 
  as 
  far 
  east 
  as 
  these 
  outlying 
  masses 
  and 
  doubtless 
  far 
  be- 
  

   yond 
  over 
  the 
  regions 
  of 
  Massachusetts 
  and 
  the 
  Connecticut 
  valley. 
  

   The 
  bold 
  outcropping 
  edges 
  of 
  thick 
  Devonic 
  strata 
  facing 
  the 
  Mo- 
  

   hawk 
  valley 
  and, 
  in 
  the 
  Helderberg 
  escarpment, 
  the 
  Ontario 
  plain, 
  

   make 
  it 
  certain 
  that 
  the 
  strata 
  formerly 
  extended 
  some 
  distance 
  

   farther 
  northward. 
  It 
  is 
  more 
  than 
  likely 
  that 
  this 
  northward 
  ex- 
  

   tension 
  of 
  Devonic 
  rocks 
  was 
  not 
  beyond 
  the 
  southern 
  border 
  of 
  

   the 
  Adirondacks 
  ; 
  at 
  least 
  we 
  have 
  no 
  positive 
  knowledge 
  that 
  the 
  

   Devonic 
  sea 
  ever 
  covered 
  any 
  of 
  northern 
  New 
  York 
  (see 
  figure 
  

  

  18). 
  

  

  There 
  was 
  no 
  disturbance 
  of 
  any 
  kind 
  at 
  the 
  close 
  of 
  the 
  Siluric, 
  

   so 
  that 
  period 
  passed 
  very 
  quietly 
  into 
  the 
  Devonic. 
  The 
  Oriskany 
  

   sandstone 
  was 
  for 
  many 
  years 
  regarded 
  as 
  the 
  base 
  of 
  the 
  Devonic 
  

   but 
  now, 
  as 
  a 
  result 
  of 
  a 
  careful 
  study 
  of 
  the 
  fossils, 
  the 
  line 
  be- 
  

   tween 
  Siluric 
  and 
  Devonic 
  is 
  drawn 
  just 
  below 
  the 
  Helderberg 
  lime- 
  

  

  